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Dictionary of networking


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  • 1. IntroductionNetworks are currently one of the fastest growing and most important developments inthe computer industry. Not only are more and more PCs becoming parts of networks, butnetworked PCs are being incorporated into larger enterprise-wide applications so that ev-eryone in a company can access and share data.With the expanding technology of networking comes the terminology to describe it.This Dictionary of Networking provides definitions for all the terms you will encounterwhen dealing with networks of any type.Who Should Use This Book?This book is designed to meet the needs of people who work with networks, communica-tions, and mobile computing systems. Whether you are networking previously uncon-nected computers or downsizing from a mainframe, this book is for you. And if you arestudying for one of the network certification exams, you will find this book to be an es-sential reference.Network users of all levels are barraged with an almost bewildering array of terms, ab-breviations, and acronyms in books, magazine and newspaper articles, advertisements,and their day-to-day conversations. Jargon is a useful shorthand, but it can easily becomeincomprehensible and unmanageable, even to the most seasoned network administrator.What You’ll Find in This BookAlong with clear explanations of the jargon and slang associated with networking, you’llfind definitions of more than 3,000 networking technical terms, abbreviations, and acro-nyms. The list that follows gives you a brief overview of the topics that this book covers:IAcronyms and abbreviationsIActive DirectoryIActiveXIApplication softwareICables, cards, and connectorsICertification schemesIChips, memory, and adaptersICommunications2461book Page i Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 2. IntroductioniiIConnectivity tools, products, and equipmentIDisks and storage mediaIE-mailIHardwareIFile systemsIIndustry standardsIInternet organizationsIInternet terms and abbreviationsIIntranet terms and abbreviationsIJavaILeading hardware and software companiesILinux, Free Software Foundation, GNUIMicroprocessorsIMicrosoft WindowsIMicrosoft Windows NT and NT ServerIMicrosoft Windows 2000IMobile computingINetworking theory and conceptsINovell NetWareINovell Directory ServicesIOperating systems and environmentsIThe OSI Reference ModelIPopular networking productsIProtocols and interfacesISecurity and network administrationISystem architecturesITrade associations2461book Page ii Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 3. iiiIntroductionIUnix shells, tools, and utilitiesIThe World Wide WebIWorkstationsHow This Book Is OrganizedThis book is organized for easy reference. Entries are arranged in letter-by-letter alphabeticorder, ignoring punctuation and spaces, with terms that begin with an uppercase letter (orare all in uppercase) before those in all lowercase letters. So Internet comes before internet,and link level comes before link-state routing algorithm. Numbers and symbols are listedat the beginning of the book in ascending numeric order. If an entry begins with a letter orletters, but contains a number, it is listed alphabetically according to the letter, and then ac-cording to numerical order, so V.42 bis comes between V.42 and V.54.The information within each entry is always presented in the following order:IEntry nameIAbbreviation or acronymIPronunciation, if it isn’t obviousIDefinition, written in clear standard EnglishIURL pointing to further resources available on the Internet.ICross-references to other entries that provide additional or related information on thetopic; more on the cross references in a moment.If an entry has multiple definitions, each one is numbered to separate it from the next,and some of the entries also contain illustrations.Extensive Cross-ReferencingThe Dictionary of Networking is the most extensively cross-referenced dictionary of com-puting and networking terms available today. It contains two kinds of cross references:IA See reference points to another entry that contains the information you are lookingfor. Thus, you can start with an abbreviation, such asPPTP, or with the complete term,such as Point-to-Point Tunneling Protocol, and be sure that you will arrive at the cor-rect definition. You don’t have to know what an abbreviation stands for to be able tolook up a term. Some terms or concepts can be referred to by more than one name, suchas dialback modem and callback modem; you will find both here, so you can alwaysfind your way to the appropriate definition.2461book Page iii Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 4. IntroductionivIA See also reference points to one or more entries that contain additional informationabout a topic. This kind of cross-reference allows you to follow through a related setof entries, broadening your search as you move from entry to entry.We have also added an extra element in this dictionary to help you find information,and that is the pronunciation of an acronym or abbreviation that is pronounced differ-ently from the way it is spelled. For example, if you are reading a magazine article andcome across the abbreviation SCSI, you can look up the abbreviation, which will pointto the main entry term, Small Computer System Interface. But if you are discussing harddisk interfaces with a colleague and hear the term scuzzy, you can look that up too, andyou will also find your way to the main entry, Small Computer System Interface.The AppendicesThis book contains four appendices to provide additional reference material:Appendix A: Internet Resources Collects together URLs under a wide variety of head-ings to cut down on the amount of time you have to spend with your favorite search en-gine. Using this appendix, you can go straight to the right Web site every time.Appendix B: Certification Resources Provides a guide through the complex and con-fusing world of computer and networking certification programs.Appendix C: ASCII Charts Contains both the standard and the extended AmericanStandard Code for Information Interchange charts.Appendix D: EBCDIC Chart Contains the most widely accepted Extended BinaryCoded Decimal Interchange Code chart.A Note about the URLs in This BookNothing is more annoying than a dead URL, and link rot is all pervasive. (If you don’tknow what link rot is, go look it up.) All the URLs in this book have been individuallychecked by our Technical Editor; and at the time of writing, they are all active, they allwork, and they all contain the information that I say they contain. But that is not to say thatsome of them won’t have changed by the time you try them out.The better-organized sites will simply post a link to the new site if they make substantivechanges, and you can use that new link to go right to the new or reorganized site. Othersites, such as the Microsoft Web site, reorganize themselves periodically as a part of theirhousekeeping; the information you want is still available, but you have to look in anotherplace to find it, or use the site’s built-in search engine to find it.2461book Page iv Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 5. vIntroductionSome of the sites that contain the most advanced technical information belong to domain and are usually computer science departments at the major universities. I havetried to keep the number of such sites to a minimum in this book. Although they can be ex-tremely useful, they usually have a lifespan that closely resembles that of the average grad-uate student. Once the student maintaining the information graduates, the site becomesneglected and is usually removed soon after. Another dead URL.To be consistent with current usage, I have not specified the protocol used to access eachWeb site; unless a different protocol is specified, you can simply assume that HTTP willwork in all cases. Just add http:// to the beginning of each Web address in your browserwhen you access a site.And finally, we have tried very carefully not to break a URL across a line; you shouldbe able to type the characters you see without having to worry about whether to type thathyphen. If a URL has to break, the break is before a period (.) or after a slash (/).About the Companion CDThe companion CD contains an electronic version of this entire book. You can use it to findentries quickly and follow cross-references without a great deal of page flipping.And Finally…Through more than 25 years of hands-on involvement in practical computer applications,including the management of minicomputer systems, PC-based networks, large-scale datacommunications systems, software development, and technical support, I have become in-timately familiar with computer and networking terminology. TheDictionary of Network-ing is a direct result of that experience, and it represents a practical and down-to-earthapproach to computers and computing.Everyone who has worked on this dictionary has tried to make sure that it is as completeand accurate as possible. But if you think that we have missed a word or two that shouldbe included in a future edition, or if you think that an entry doesn’t contain enough infor-mation, please write to the following address:Dictionary of Networkingc/o SYBEX Inc.1151 Marina Village ParkwayAlameda, CA 94501-1044USA2461book Page v Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 6. 14.4BSD LiteSymbols and Numbers! See bang.& See ampersand.* See asterisk.*.* See star-dot-star.. See period and double-perioddirectories... See period and double-perioddirectories./ See slash.// See double-slash.: See colon.<> See angle brackets.> See right angle bracket.? See question mark.@ See at symbol. See backslash.| See vertical bar.1/4-inch cartridge See quarter-inchcartridge.2B+D Common abbreviation for BasicRate ISDN, which has two B, or bearer,channels and one D, or data, channel.See also 23B+D; Basic Rate ISDN.3+ A network operating system, originallydeveloped by 3Com, that implemented Xe-rox Network System (XNS) transport pro-tocols and Microsoft MS-Net file sharing.3Com Corporation One of the largestmanufacturers of network hardware in theworld, particularly known for LAN andWAN products, including remote accessproducts, hubs, network interface cards,Gigabit Ethernet, and multimedia over net-works. The company’s PalmPilot hand-held computer has proved to be extremelypopular, with more than one million unitssold to date. In 1997, 3Com merged withU.S. Robotics in a deal worth $6.6 billion.For more information on 3Com, encoding A data-translationscheme used to precede signal encoding inFDDI (Fiber Distributed Data Interface)networks. In 4B/5B, each group of four bitsis represented as a five-bit symbol, which isthen associated with a bit pattern, which inturn is encoded using a standard method,often NRZI (non-return to zero inverted).See also Manchester encoding.4.4BSD Lite A version of the 4.4 Berke-ley Software Distribution (BSD) Unix fromwhich all the AT&T code has been re-moved in an attempt to avoid licensingconflicts. It is not possible to compile andthen run 4.4BSD Lite without a preexistingsystem because several important utilitiesand other files from the operating systemare missing.The 4.4BSD Lite version has served as thebasis for several other important Uniximplementations, including FreeBSD andNetBSD.2461book Page 1 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 7. 5B/6B encoding2See also Berkeley Software DistributionUnix; FreeBSD; NetBSD; Unix.5B/6B encoding A data-translationscheme used to precede signal encoding in100BaseVG networks. In 5B/6B, eachgroup of five bits is represented as a six-bitsymbol, which is then associated with a bitpattern, which in turn is encoded using astandard method, often NRZI (non-returnto zero inverted).See also Manchester encoding.9-track tape A tape storage format thatuses nine parallel tracks on 1/2-inch, reel-to-reel magnetic tape. Eight tracks are usedfor data, and one track is used for parity in-formation. These tapes are often used asbackup systems on minicomputer andmainframe systems; digital audio tapes(DATs) are more common on networks.See also quarter-inch cartridge.10/100 A term used to indicate that a de-vice can support both Ethernet (at a datatransfer rate of 10Mbps) and Fast Ethernet(at a data transfer rate of 100Mbps).See also Ethernet.10Base2 An implementation of the 802.3Ethernet standard on thin Ethernet (RG-58)coaxial cable; sometimes called thinnet orcheapernet wire. The 10Base2 specificationhas a data-transfer rate of 10Mbps and amaximum cable-segment length of 185meters (610.5 feet). A T-connector attachesthe thin coaxial cable to the BNC connectoron the Ethernet adapter.10Base5 An implementation of the802.3 Ethernet standard on thick Ethernetcoaxial cable; sometimes called thicknet.The 10Base5 specification has a data-trans-fer rate of 10Mbps and a maximum cable-segment length of 500 meters (1650 feet),over a bus topology. The cable attaches tothe Ethernet adapter with a vampire, orpiercing, connector and a transceiver.See also bus network.10BaseF An implementation of the802.3 Ethernet standard over fiber-opticcable. This specification allows throughputof a maximum of 10Mbps and is separatedinto these three categories:I10BaseFP (fiber passive) Used for desk-top connectionsI10BaseFL (fiber link) For intermediatehubs and workgroupsI10BaseFB (fiber backbone) Used forcentral facility lines between buildings10BaseT An implementation of the802.3 Ethernet standard over UTP wir-ing—the same wiring and RJ-45 connectorsused with telephone systems. The standardis based on a star topology, with each nodeconnected to a central wiring center and amaximum cable-segment length of 100meters (330 feet).See also star network.23B+D Common abbreviation for Prima-ry Rate ISDN, which has 23 B, or bearer,channels and 1 D, or data, channel.See also 2B+D; Primary Rate ISDN.24/7 Abbreviation for round-the-clockavailability, implying that the service isavailable 24 hours a day, 7 days a week.2461book Page 2 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 8. 3802.x56K modem standard See V.90.100Base-FX A specification for FastEthernet over fiber-optic cable.See also Fast Ethernet100Base-T4 A specification for FastEthernet over four pairs of Category 3, 4, or5 untwisted-pair wiring.See also Fast Ethernet100Base-TX A specification for FastEthernet over two pairs of Category 5unshielded twisted-pair or Category 1shielded twisted-pair cable. The 100Base-TX specification requires two pairs ofwires.See also Fast Ethernet100VG-AnyLAN A term applied to theIEEE 802.12 standard, originally developedby Hewlett-Packard and supported by Nov-ell, Microsoft, AT&T, and many others.The 100VG-AnyLAN specification modi-fies the existing Ethernet standard to allowspeeds of 10 or 100Mbps and uses thedemand priority access method ratherthan Carrier Sense Multiple Access/Colli-sion Detection (CSMA/CD). A speed of100Mbps transmission is supported overCategory 3 four-pair unshielded twisted-pair cabling.See also demand priority; Fast Ethernet.680x0 A family of 32-bit microproces-sors from Motorola, used in Macintoshcomputers and many advanced worksta-tions. The 680x0 is popular with program-mers, because it uses a linear-addressingmode to access memory, rather than thesegmented-addressing scheme used by Intelcoprocessors.Several models have been developed:I68000 The first microprocessor in thisfamily, which used a 32-bit data wordwith a 16-bit data bus and could address16MB of memory. It was used in the firstApple Macintosh computers as well as inHewlett-Packard’s LaserJet printers.I68020 A 32-bit microprocessor thatruns at 16MHz, 20MHz, 25MHz, or33MHz and is capable of addressing asmuch as 4GB of memory. The 68020 wasused in the Macintosh II computer, buthas been replaced by the 68030.I68030 Has a paged memory manage-ment unit built-in and, therefore, does notneed external hardware to handle thisfunction. The 68030 is used in the Mac-intosh II and SE computers.I68040 Incorporates a built-in floating-point processor and memory manage-ment unit, along with independent 4KBdata and instruction caches. It can per-form parallel execution by using multiple,independent instruction queues. The68040 is used in the Macintosh Quadraline of computers.See also PowerPC.802.x A set of communications standardsdefining the physical and electrical connec-tions in LANs, originally defined by the In-stitute of Electrical and ElectronicsEngineers (IEEE).A number followed by an uppercase letterindicates a stand-alone standard; a num-ber followed by a lowercase letter indicates2461book Page 3 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 9. 802.14either a supplement to a standard or a partof a multiple-number standard.Many of the IEEE standards have also beenadopted by the International Organizationfor Standardization(ISO), whose standardsare accepted all over the world; IEEE stan-dards 802.1 to 802.11 are now also knownas ISO 8802.1 to 8802.11. You will seeboth designations in networking books andmagazines; it will take a while for everyoneto get used to these numbers.See also IEEE standards.802.1 An IEEE standard that specifiesthe media-access-control level for bridgeslinking 802.3, 802.4, and 802.5 networks.It includes a spanning-tree algorithm forEthernet media-access-control layer bridg-es and the heterogeneous LAN manage-ment specification for Ethernet and token-ring hubs.See also IEEE standards.802.2 An IEEE standard that specifies thelogical linksublayerof the data-link layer inthe OSI protocol stack. The data-link layerin the OSI protocol stack is divided into thelogical link layer and the media-access-con-trol layer. The logical link layer providesframing, addressing, and error-controlfunctions.See also IEEE standards.802.3 An IEEE standard for CSMA/CD(Carrier Sense Multiple Access/Collision De-tection) LANs, including both baseband andbroadband networks. The baseband versionis based on the Ethernet network, originallydeveloped by Xerox Corporation.The 802.3 standard includes the following:I10Base2 An implementation of theEthernet standard on thin Ethernet cable,with a data-transfer rate of 10Mbps and amaximum cable-segment length of 185meters (600 feet).I10Base5 An802.3Ethernetstandardonthick Ethernet cable, with a 10Mbps data-transfer rate and a cable-segment lengthof a maximum of 500 meters (1650 feet),over a bus topology.I10BaseT Establishes a standard forEthernet over UTP wiring, the same wir-ing and RJ-45 connectors used with tele-phone systems. The standard is based ona star topology. Each node is connected toa wiring center, with a cable-length limi-tation of 100 meters (330 feet).I1Base5 A 1Mbps network standardwith twisted-pair cable based on AT&T’sStarLAN.I10Broad36 Defines a long-distanceEthernet with a 10Mbps data-transferrate and a maximum cable-segmentlength of 3600 meters (11,880 feet).I10BaseF Explicitly specifies fiber-opticcable in three settings; 10Base-FP (fiberpassive) for desktops, 10Base-FL (fiberlink) for intermediate hubs and work-groups, and 10Base-FB (fiber backbone)for central facility lines between buildings.I100BaseVG A 100Mbps Ethernet net-work developed by Hewlett-Packard andAT&T Microelectrics.I100BaseT A 100Mbps Ethernet devel-oped by Grand Junction Networks.See also 100VG-AnyLAN; Ethernet; FastEthernet; Gigabit Ethernet; IEEE standards.2461book Page 4 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 10. 51394802.4 An IEEE standard for bus topolo-gy networks that use token passing to con-trol access and network traffic, running at10Mbps a second. Token-bus networksare sometimes used in manufacturing set-tings, but they are not often found in officenetworks.See also ARCnet; IEEE standards; Techni-cal and Office Protocol.802.5 An IEEE standard that defines ringnetworks using token passing to control ac-cess and network traffic, running at 4 or16Mbps. It is used by IBMs Token Ringnetwork over STP, UTP, or fiber-opticcabling. Also known as ANSI 802.1-1985.See also IEEE standards.802.6 An IEEE standard for metropoli-tan-area networks (MANs). It describes aDQDB (Distributed Queue Dual Bus) usedfor transmitting voice, video, and data overtwo parallel fiber-optic cables, with signal-ing rates in excess of 100Mbps per second.See also IEEE standards; Switched Multi-megabit Data Services.802.7 An IEEE Technical Advisory Group(TAG) report on broadband networks car-rying voice, data, and video traffic.See also IEEE standards.802.8 An IEEE Technical AdvisoryGroup (TAG) report on the use of fiber op-tics as alternatives to copper-based cable inLANs.See also IEEE standards.802.9 An IEEE advisory committee on in-tegrated data, voice, and video networking.The specification has been called IVD (In-tegrated Voice and Data), but is now morecommonly referred to as Iso-Ethernet.See also IEEE standards; Iso-Ethernet.802.10 An IEEE Technical AdvisoryGroup (TAG) working on the definition ofa standard security model for use over a va-riety of network types that incorporates au-thentication and encryption methods.See also IEEE standards.802.11 A proposed IEEE standard thatwill define wireless LANs, includingspread-spectrum radio, narrowband radio,infrared transmission, and transmissionover power lines.See also IEEE standards.802.12 An IEEE working group definingthe 100Mbps Ethernet 100VG-AnyLANoriginally developed by Hewlett-Packardand several other vendors.See also 100VG-AnyLAN; IEEE standards.802.14 An IEEE working group definingstandards for data transmission over tra-ditional cable TV networks using cablemodems.See also IEEE standards.1394 An IEEE standard for a digital plug-and-playbus,originallyconceivedbyAppleComputer in 1986. The 1394 standard sup-ports a maximum of 63 nodes per bus anda maximum of 1023 buses.Three speeds for device connections areavailable:I100Mbps2461book Page 5 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 11. 32706I200MbpsI400MbpsAll devices are hot pluggable, and both self-powered and bus-powered devices can beattached to the same bus. Also known asFireWire, 1394 uses six-pair shieldedtwisted-pair cable and is intended for high-end applications such as digitized video.See also Universal Serial Bus.3270 A general description for the familyof products from IBM that includes termi-nals, printers, and terminal cluster control-lers.Theseproductsallcommunicatewithamainframe computer using the SNA (Sys-tems Network Architecture) protocol.80286 Also called the 286. A 16-bit mi-croprocessor from Intel, first released inFebruary 1982, used by IBM in the IBM PC/AT computer in 1984. Since then, it hasbeen used in many other IBM-compatiblecomputers.The 80286 uses a 16-bit data word and a16-bit data bus, with 24 bits to addressmemory. It has two modes:IReal mode effectively limits performanceto that of an 8086 microprocessor and canaddress 1MB of memory.IProtected mode prevents an applicationfrom stopping the operating system be-cause of an error and can address 16MBof memory.80386 Also called the 386DX and the386. A full 32-bit microprocessor intro-duced by Intel in October 1985 and used inmany IBM and IBM-compatible comput-ers. The 80386 has a 32-bit data word, cantransfer information 32 bits at a time overthe data bus, and can use 32 bits in address-ing memory. It has the following modes:IReal mode effectively limits performanceto that of an 8086 microprocessor and canaddress 1MB of memory.IProtected mode prevents an applicationfrom stopping the operating system be-cause of an error, and it can address 4GBof memory.IVirtual 8086 mode allows the operatingsystem to divide the 80386 into severalvirtual 8086 microprocessors, all runningwith their own 1MB of space, and all run-ning a separate program.80486 Also called the 486 or i486. A 32-bit microprocessor introduced by Intel inApril1989.The80486addsseveralnotablefeatures to the 80386, including an on-board cache, a built-in floating-point pro-cessor, and a memory management unit(MMU), as well as advanced provisions formultiprocessing and a pipelined executionscheme.2461book Page 6 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 12. 7accelerator boardAA+ Certification Acertificationprogramfrom the CompTIA (Computer TechnologyIndustry Association) designed to measurecompetence in basic computer repair andaimed at the computer technician. Certifi-cation requires passing two tests: a coreexam to test general knowledge of PCs, in-cluding configuration, installation and up-grading, diagnosis, repair, maintenance,customer interaction, and safety, and atleast one specialty exam that tests operatingsystem knowledge.A+B signaling A type of in-band signal-ing used in T1 transmission; 1 bit from eachof the 24 subchannels in every sixth frame isused to carry dialing and other control infor-mation. A+B signaling reduces the T1 band-width from 1.544Mbps to 1.536 Mbps.See also T1.a-b box A switching box that allows twoor more computers to share a peripheral de-vice such as a printer. It can be switchedmanually or through software.A/UX A version of the Unix operatingsystem that runs on the Macintosh. A/UX isbased on the System V release 2 of Unix andincludes a number of Apple features, suchassupportfortheMacintoshToolbox.Thissupport allows applications running underA/UX to use the familiar Macintosh user in-terface. You need a Macintosh II with aMotorola 68020 or higher microprocessorand at least 4MB of memory to use A/UX.See also Unix.AAL See ATM Adaptation Layer.AASE See Associate AccreditedSystems Engineer.ABCP See Associate BusinessContinuity Professional.abend Contraction of abnormal end. Amessage issued by an operating system whenit detects a serious problem, such as a hard-ware failure or major software damage.ABI See Application Binary Interface.ABR See Available Bit Rate.ABUI See Association of Banyan UsersInternational.accelerator board An add-in, printedcircuit board that replaces the main proces-sor with a higher-performance processor.Using an accelerator board can reduce up-grading costs substantially, because youdon’t need to replace the monitor, case,keyboard, and so on. However, the mainprocessor is not the only component that af-fects the overall performance of your sys-tem. Other factors, such as disk-access timeand video speed, contribute to a system’sperformance.See also graphics accelerator board.2461book Page 7 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 13. access8access To use, write to, or read from afile, or to log in to a computer system ornetwork.AccessBuilder Remote access softwarefrom 3Com Corporation that lets you ac-cess network resources over a dial-up con-nection from a remote location.access control entry AbbreviatedACE. The basic unit of security in Mi-crosoft Windows 2000 that controls accessto the file system, to Active Directory ob-jects, to printers and other network re-sources, and to the Registry.An ACE consists of a security identifier(SID) and an access mask that defines theaccess rights of that SID. A collection ofACEs that control access to an object isknown as an access control list.See also access control list; securityidentifier.access control list Abbreviated ACL. Alist or table containing information aboutthe users, processes, and objects that can ac-cess a specific file or object. ACLs are usu-ally attached to file-system directories, andthey specify access permissions such asread, write, execute, delete, and so on.ACLs are implemented in Novell NetWare,Microsoft Windows 2000, and Unix:IIn Novell Directory Services, ACLs are as-sociated with every object in the NDS tree,storing the list of rights for each trusteethat can access the object.IIn the Unix Network File System, ACLsinclude the name of the user or group,along with the rights granted to that useror group.IInWindows2000, everythingisanobject,and every object has an associated ACL.See also Active Directory; authentication;NDStree;NovellDirectoryServices;rights;security.access method The set of rules that de-termines which node in a network has ac-cess to the transmission media at anymoment.Attempts at simultaneous access are eithermanaged by a collision detection mecha-nism such as CSMA/CD or prevented byuse of a token-passing method.access protocol The set of rules thatworkstations use to avoid collisions whensending information over shared networkmedia. Also known as the media access con-trol protocol.access rights See rights.access server A computer that providesaccess for remote users who dial in to thesystem and access network resources asthough their computers were directly at-tached to the network.See also communications/modem server;mobile computing.access time The period of time thatelapses between a request for informationfrom disk or memory and the arrival of thatinformation at the requesting device.Memory-access time refers to the time ittakes to transfer a character between mem-ory and the processor. Disk-access time2461book Page 8 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 14. 9ACFrefers to the time it takes to place the read/write heads over the requested data. RAMmay have an access time of 80 nanosecondsor less, while hard-disk access time could be10 milliseconds or less.access token In Microsoft Windows2000, an object that contains the securityidentifier (SID) of a running process.When a process is started by another pro-cess, the second process inherits the startingprocess’s access token. This access token isthen checked against each object’s accesscontrol list to confirm that the appropriatepermissions are in place to permit any ser-vices requested by the process.See also access control list; permissions;process; rights.account OnLANsormultiuseroperatingsystems, an account is set up for each user.Accounts are usually kept for administrativeor security reasons. For communicationsand online services, accounts identify a sub-scriber for billing purposes.See also user account.accounting The process of tracking theresources on a network. The network ad-ministrator can charge for files accessed,connect time, disk space used for file stor-age, and service requests by assigning ac-count balances to users. The users can thendraw from their account balances as theyuse network services.account lockout In Microsoft Windows2000 and other operating systems, a countof the number of invalid logon attempts al-lowed before a user is locked out.See also authentication; user account.account policy On networks and mul-tiuser operating systems, the set of rulesthat defines whether a new user is permittedaccess to the system and whether an exist-ing user is granted additional rights or ex-panded access to other system resources.Account policy also specifies the minimumlength of passwords, the frequency withwhich passwords must be changed, andwhether users can recycle old passwordsand use them again.Accredited Systems Engineer Abbre-viated ASE. A certification from Compaqdesigned to evaluate and recognize exper-tise in installing and administering Compaqworkstations and servers running both Mi-crosoft Windows 2000 and Novell Net-Ware network operating systems.See also Associate Accredited SystemsEngineer.ACE See access control entry.Acer Group One of the top five PC mak-ers in the world, with factories in Malaysia,the Netherlands, the Philippines, Taiwan,and the United States. The Acer Groupbought Texas Instrument’s notebook com-puter business in 1997 and has formed busi-ness alliances with companies, including3Com and Hitachi, for the development ofadvanced digital consumer products suchas PC-ready televisions and DVD systems.For more information on the Acer Group,see See Advanced CommunicationsFunction.2461book Page 9 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 15. ACK10ACK See acknowledgment.acknowledgment Abbreviated ACK. Incommunications, ACK is a control code,ASCII 06, sent by the receiving computer toindicate that the data has been receivedwithout error and that the next part of thetransmission may be sent.See also NAK.ACL See access control list.ACONSOLE A Novell NetWare 3.xworkstation utility that controls a modemattached to the workstation. ACONSOLE isused to establish an asynchronous remoteconsole connection to a server. The RS232NetWare Loadable Module (NLM) must beloaded on the server to which you want toconnect. In NetWare 4.x, use RCONSOLEto perform this function.acoustic coupler A modem that in-cludes a pair of rubber cups that fit over themouthpiece and earpiece of a standard tele-phone handset (to prevent external noisefrom being picked up). An acoustic couplerallows you to connect your computer to atelephone system that does not have thestandard RJ-11 connections used with con-ventional modems.ACPI See Advanced Configuration andPower Interface.ACR See Available Cell Rate.across-the-wire migration A methodof migrating file-server data, trustee rights,and other information to a Novell Net-Ware server using the NetWare Migrationutility. You can also use across-the-wiremigration to upgrade from LAN Manager,LAN Server, and earlier versions of Net-Ware; a similar process known as BMI-GRATE allows users to migrate fromBanyan VINES.ACS See Advanced CommunicationsService.ACTE See Ascend Certified TechnicalExpert.Active Desktop In Microsoft Windows,a user interface feature that makes the Desk-top look and behave just like a Web page,with underlined icons and a hand mousepointer. Active Desktop is offered as an al-ternative to the classic Windows user inter-face; you can use Active Desktop, you canuse the classic Windows interface, or youcan swap back and forth between the two.Active Directory InMicrosoftWindows2000, a system for large-scale networkmanagement that views the network as a hi-erarchy of objects. Active Directory doesthe following:IProvides a hierarchy for the managementof all network objects, including users,servers, services, file shares, Web pages,printers, and so on.IDivides administration and security intosubdomains, domains, and trees ofdomains.IScales to 10 million users per domain.IImplementsMIT’sKerberosauthenticationsystembasedonprivatekeyencryptionandalso supports public key encryption forauthentication of clients and businesspartners.2461book Page 10 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 16. 11active terminationIEmulates Windows NT 4.x directory ser-vices for backward compatibility.IUses DNS rather than WINS, and requiresall user and host names to be in DNSform.IUses LDAP rather than a proprietary pro-tocol so that non-Microsoft applicationscan query the name database.IInteroperates with Novell NetWare Di-rectory Services.See also forest; Kerberos; Lightweight Di-rectory Access Protocol; NetWare Directo-ry Services; Microsoft Windows 2000; tree.Active Directory Service InterfaceAbbreviated ADSI. In Microsoft Active Di-rectory, an application programming inter-face (API) designed to simplify access toActive Directory objects.See also Active Directory; application pro-gramming interface.Active Directory Users andComputers Abbreviated ADUC. In Mi-crosoft Windows 2000 Server, the main ad-ministrative tool used to manage useraccounts, security groups, organizationalunits, and policies.ADUC is a Microsoft Management Con-sole (MMC) snap-in and replaces WindowsNT User Manager.See also Active Directory; Microsoft Man-agement Console; hub A device that amplifies trans-mission signals in a network, allowing sig-nals to be sent over a much greater distancethan is possible with a passive hub.An active hub may have ports for coaxial,twisted-pair, or fiber-optic cable connec-tions, as well as LEDs to show that eachport is operating correctly.See also repeater.Active Monitor The first station to bestarted on a Token Ring network. The Ac-tive Monitor is responsible for passing andmaintaining the token and detects error con-ditions. The Active Monitor’s performanceis constantly monitored by the StandbyMonitorSee also Standby Monitor.Active Server Pages Abbreviated ASP.In Microsoft Internet Information Server, ascript interpreter and execution environ-ment that supports VBScript and Java-Script and is compatible with other script-ing languages such as Perl, REXX, Tcl, andPython through add-ins from third-partydevelopers.ASP allows you to combine HTML, scripts,and ActiveX components on the same Webserver; all the code runs on the server andpresents the results of this dynamic processto the client browser as a standard HTMLpage.See also JavaScript; Perl; Tcl; termination A technique used toterminate a SCSI. Active termination reduc-es electrical interference in a long string ofSCSI devices.See also forced perfect termination; pas-sive termination.2461book Page 11 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 17. active window12active window The window currentlyaccepting mouse clicks and keyboard input.The title bar of the active window is alwaysa different color from that of the other openwindows.ActiveX The latest development of Mi-crosoft’s COM, the foundation that sup-ported OLE. By adding network capabilities(and so creating DCOM, or DistributedCOM) and by reducing the scope of OLE tocreate ActiveX, Microsoft has created acomprehensive set of component-basedInternet- and intranet-oriented applications.In an attempt to promote ActiveX as a stan-dard, in 1996 Microsoft turned over con-trol of ActiveX to the Open Group tomanage future developments.See also ActiveX control; Distributed Com-ponent Object Model; Java.ActiveX control The basic buildingblock of Microsoft’s ActiveX specification.An ActiveX control is a software modulethat cannot run by itself, but requires an Ac-tiveX container such as a Web browser, aword processor, or a spreadsheet. Eachcontrol delivers a specific function such asdatabase access, user-interface elements, orfile access and can communicate with an-other ActiveX control, an ActiveX contain-er, or the underlying Windows operatingsystem.Unlike Java applets, which for security rea-sons run in a sandbox designed to protectthe file system from unauthorized access,ActiveXcandirectlyaccessfiles.Toprovidea measure of security, ActiveX controls arepackagedwithdigitalcertificatesthatprovethe origin of the control.See also ActiveX; certificate; Java; Javaapplet; Java Virtual Machine; sandbox.AD See Active Directory.Adaptec, Inc. A leading manufacturer ofhigh-performance networking and connec-tivity products, including SCSI adapters,RAID products, Fast Ethernet adapters,ATM network interface cards, and servermanagement software. In 1998, Adaptecacquired Ridge Technologies, a manufac-turer of RAID and other storage solutionsfor Microsoft Windows 2000.For more information on Adaptec, A printed circuit board thatplugs into a computer’s expansion bus toprovide added capabilities.Common adapters include video adapters,joy-stick controllers, and I/O adapters, aswell as other devices, such as internal mo-dems, CD-ROMs, and network interfacecards. One adapter can often support sev-eral different devices. Some of today’s PCdesigns incorporate many of the functionspreviously performed by these individualadapters on the motherboard.adaptive equalization See adaptivespeed leveling.adaptive routing A mechanism that al-lows a network to reroute messages dynam-ically, using the best available path, if aportion of the network fails.See also alternative route.adaptive speed leveling A modemtechnology that allows a modem to respond2461book Page 12 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 18. 13address classesto changing line conditions by changing itsdata rate. As line quality improves, the mo-dem attempts to increase the data rate; asline quality declines, the modem compen-sates by lowering the data rate. Also knownas adaptive equalization.ADCCP See Advanced Data Communi-cations Control Procedures.address 1. The precise location in mem-ory or on disk where a piece of informationis stored. Each byte in memory and eachsector on a disk has its own unique address.2. The unique identifier for a specific nodeon a network. An address may be a physicaladdress specified by switches or jumpers onthe network interface card hardware, or itcan be a logical address established by thenetwork operating system.3. To reference or manage a storagelocation.4. In Unix, an IP address as specified in the/etc/hosts file.5. Information used by a network or the In-ternet to specify a specific location in theform username@hostname; username isyour user name, logon name, or accountname or number, and hostname is the nameof the Internet Service Provider (ISP) orcomputer system you use. The hostnamemay consist of several parts, each separatedfrom the next by a period.See also address bus; Domain Name Ser-vice; e-mail address; Internet Service Pro-vider; IP address; memory address.address bus The electronic channel,usually from 20 to 64 lines wide, used totransmit the signals that specify locations inmemory.The number of lines in the address bus de-termines the number of memory locationsthat the processor can access, because eachline carries one bit of the address. A 20-lineaddress bus (used in early Intel 8086/8088processors) can access 1MB of memory, a24-line address bus can access 16MB, and a32-line address bus can access more than4GB. A 64-line address bus (used in theDEC Alpha APX) can access 16EB.address classes In a 32-bit IP address,which is shown in the accompanying illus-tration, the number of bits used to identifythe network and the host vary accordingto the network class of the address, asfollows:IClass A is used only for very large net-works. The high-order bit in a Class Anetwork is always zero, leaving 7 bitsavailable to define 127 networks. The re-maining 24 bits of the address allow eachClass A network to hold as many as16,777,216 hosts. Examples of Class Anetworks include General Electric, IBM,Hewlett-Packard, Apple Computer,Xerox, Digital Equipment Corporation,and MIT. All the Class A networks are inuse, and no more are available.IClass B is used for medium-sized net-works. The 2 high-order bits are always10, and the remaining bits are used to de-fine 16,384 networks, each with as manyas 65,535 hosts attached. Examples ofClass B networks include Microsoft andExxon. All Class B networks are in use,and no more are available.2461book Page 13 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 19. addressing space14IClass C is for smaller networks. The 3high-order bits are always 110, and the re-maining bits are used to define 2,097,152networks, but each network can have amaximum of only 254 hosts. Class C net-works are still available.IClass D is a special multicast address andcannot be used for networks. The 4 high-order bits are always 1110, and the re-maining 28 bits allow for more than 268million possible addresses.IClass E is reserved for experimental pur-poses. The first four bits in the address arealways 1111.See also Classless Inter-Domain Routing;IP address; subnet mask.IP ADDRESS STRUCTUREaddressing space The amount of RAMavailable to the operating system runningon a server.address mask See subnet mask.Address Resolution Protocol Abbrevi-ated ARP. A protocol within TCP/IP(Transmission Control Protocol/InternetProtocol) and AppleTalk networks that al-lows a host to find the physical address of anode on the same network when it knowsonly the target’s logical or IP address.Under ARP, a network interface card con-tains a table (known as the address resolu-tion cache) that maps logical addresses tothe hardware addresses of nodes on the net-work. When a node needs to send a packet,it first checks the address resolution cacheto see if the physical address information isalready present. If so, that address is used,and network traffic is reduced; otherwise, a2461book Page 14 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 20. 15Advanced Communications Servicenormal ARP request is made to determinethe address.See also IP address.address translation gateway Abbrevi-ated ATG. A function in Cisco DECnetrouting software capable of establishing auser-specified address translation mecha-nism for certain selected nodes on the net-work.adjacency A term describing the rela-tionship formed between certain neighbor-ing routers for the purpose of swappingrouting information. Adjacency is based onthe use of a common network segment.administrative alerts In Windows2000, informational messages sent to spe-cific accounts, groups, or computers to an-nounce security events, impendingshutdown due to loss of server power, per-formance problems, and printer errors.When a server generates an administrativealert, the appropriate message is sent to apredefined list of users and computers.See also Alerter service.administrative distance A term usedby Cisco Systems, Inc., to express theintegrity of a routing-information source.Administrative distance is expressed as avalue in the range 0 through 255; the higherthe value, the lower the quality of the rout-ing information.Administrator account In MicrosoftWindows 2000, a special account with themaximum authority and permissions thatcan assign any permission to any user orgroup.The Administrator account cannot be delet-ed, but it can be renamed, which is probablya good security policy.See also permissions.ADMIN object A NetWare DirectoryServices User object, created during the in-stallation of NetWare, that has special priv-ileges, including the supervisory rights tocreate and manage other objects.ADMIN has Supervisor rights and can,therefore, manage the NetWare DirectoryServices tree and add or delete Directoryobjects.ADSI See Active Directory ServiceInterface.ADSL See Asymmetric Digital Sub-scriber Line.ADUC See Active Directory Users andComputers.Advanced CommunicationsFunction Abbreviated ACF. A set ofprogram packages from IBM that allowscomputer resources to be shared overcommunications links using the concepts ofSAA (Systems Application Architecture).For example, ACF/TCAM (Advanced Com-munications Functions/Telecommunica-tions Access Method) and ACF/VTAM(Advanced Communications Functions/Vir-tual Telecommunications Access Method)allow the interconnection of two or more do-mains into one multiple-domain network.Advanced Communications ServiceAbbreviated ACS. A large data-communi-cations network established by AT&T.2461book Page 15 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 21. Advanced Configuration and Power Interface16Advanced Configuration and PowerInterface Abbreviated ACPI. An inter-face specification developed by Intel, Mi-crosoft, and Toshiba for controlling poweruse on the PC and all other devices at-tached to the system. A BIOS-level hard-ware specification, ACPI depends onspecific hardware that allows the operat-ing system to direct power managementand system configuration.See also Advanced Power Management.Advanced Data Communications Con-trol Procedures Abbreviated ADCCP.A bit-oriented, link-layer, ANSI-standardcommunications protocol.See also High-level Data Link Control.Advanced Interactive ExecutiveAbbreviated AIX. A version of Unix fromIBM that runs on its RS/6000 workstationsand on minicomputers and mainframes.Although AIX is based on Unix System VRelease 3, it contains many of the featuresavailable in System V Release 4, isPOSIX-compliant, and meets the TrustedComputer Base (TCB) Level C2 security.One of the major enhancements of AIX isVisual Systems Management (VSM), agraphical interface into the older SystemsManagement Interface Tool (SMIT). VSMcontains four main elements: Print Manag-er, Device Manager, Storage Manager, andUsers and Groups Manager.Advanced Micro Devices, Inc. Abbre-viated AMD. The fifth largest manufactur-er of integrated circuits, flash memory, andmicroprocessors, specializing in clones ofIntel’s popular PC chips, including theAMD386, AMD486, AMDK5, and theAMDK6.For more information about AMD, also Cyrix; Intel Corporation; Pentium;Pentium II; Pentium III.Advanced Mobile Phone Service Ab-breviated AMPS. Currently the cellulartelephone standard in the United States; ananalog, cellular communications system de-veloped by AT&T. AMPS uses frequency-division multiplexing (FDM) and operatesin the 825 to 890MHz range.See also Cellular Digital Packet Data.Advanced Peer-to-Peer Internet-working An SNA routing scheme pro-posed by Cisco Systems and eventuallyabandoned.Advanced Peer-to-Peer NetworkingAbbreviated APPN. IBM’s SNA (SystemsNetwork Architecture) protocol, based onAPPC (Advanced Program-to-ProgramCommunications). APPN allows nodes onthe network to interact without a main-frame host computer and implements dy-namic network directories and dynamicrouting in an SNA network.APPN can run over a variety of network me-dia, including Ethernet, token ring, FDDI,ISDN, X.25, SDLC, and higher-speed linkssuch as B-ISDN or ATM.See also Asynchronous Transfer Mode;Customer Information Control System;Systems Network Architecture.Advanced Power Management Ab-breviated APM. An API specification from2461book Page 16 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 22. 17Aggregate Route-Based IP SwitchingMicrosoft and Intel intended to monitorand extend battery life on a laptop comput-er by shutting down certain system compo-nents after a period of inactivity.See also Advanced Configuration andPower Interface.Advanced Program-to-ProgramCommunications AbbreviatedAPPC.Aset of protocols developed by IBM as a partofitsSNA(SystemsNetworkArchitecture),designed to allow applications running onPCs and mid-range hosts to exchange dataeasily and directly with mainframes. APPCcan be used over an SNA, Ethernet, X.25,or Token Ring network and is an open,published communications protocol.APPC/PC is a PC-based version of APPCused over a Token Ring network.advanced run-length limitedencoding Abbreviated ARLL. A tech-nique used to store information on a harddisk that increases the capacity of run-length limited (RLL) storage by more than25 percent and increases the data-transferrate to 9Mbps.See also RLL encoding.Advanced Technology AttachmentAbbreviated ATA. The ANSI X3T10 stan-dard for the disk-drive interface usuallyknown as Integrated Drive Electronics(IDE).See also Integrated Drive Electronics.advertising The process by which servic-es on a network inform other devices on thenetwork of their availability. Novell Net-Ware uses the Service Advertising Protocol(SAP) for this purpose.AFP See AppleTalk Filing Protocol.AFS See Andrews File System.aftermarket The market for relatedhardware, software, and peripheral devicescreated by the sale of a large number ofcomputers of a specific type.agent 1. A program that performs a taskin the background and informs the userwhen the task reaches a certain milestone oris complete.2. A program that searches through ar-chives looking for information specified bythe user. A good example is a spider thatsearches Usenet articles. Sometimes calledan intelligent agent.3. In SNMP (Simple Network Manage-ment Protocol), a program that monitorsnetwork traffic.4. In client-server applications, a programthat mediates between the client and theserver.Aggregate Route-Based IPSwitching Abbreviated ARIS. A schemefrom IBM used to establish switched pathsthrough networks that act as virtual cir-cuits, transmitting data packets through thenetwork without the need to make routingdecisions at every step. ARIS uses taggingtechniques to add information to the datapackets that can be used to guide the pack-ets through the virtual circuits based on in-formation already established by protocolssuch as Open Shortest Path First (OSPF)and Border Gateway Protocol (BGP).2461book Page 17 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 23. AIX18AIX See Advanced InteractiveExecutive.alert log In Microsoft Windows 2000, aSystem Monitor log used to monitorcounters that exceed user-specified limits.When such a limit is exceeded, the event islogged into the alert log.See also counter log; System Monitor;trace log.Alerter service A Microsoft Windows2000 service that warns a predefined list ofusers and computers of an administrativealert. The Alerter service is used by theServer service and requires the Messengerservice.See also administrative alerts; Messengerservice; service.Alias object In Novell NetWare, a leafobject that references the original locationof an object in the directory. Using Alias ob-jects, one object can appear in several con-tainers at the same time, allowing users tolocate and use the object quickly and easily.See also leaf object.Allowed Cell Rate See Available CellRate.alphanumeric Consisting of letters,numbers, and sometimes special controlcharacters, spaces, and other punctuationcharacters.See also American Standard Code forInformation Interchange; Extended BinaryCoded Decimal Interchange Code;Unicode.alpha testing The first stage in testing anew hardware or software product, usuallyperformed by the in-house developers orprogrammers.See also beta testing.alternative route A secondary commu-nications path to a specific destination. Analternative route is used when the primarypath is not available.See also adaptive routing.alt newsgroups A set of Usenet news-groups containing articles on controversialsubjects often considered outside the main-stream. Alt is an abbreviation for alternative.These newsgroups were originally createdto avoid the rigorous process required tocreate an ordinary newsgroup. Some altnewsgroups contain valuable discussionson subjects ranging from agriculture towolves, others contains sexually explicitmaterial, and others are just for fun. Not allISPs and online services give access to thecomplete set of alt newsgroups.See also mailing list; moderatednewsgroup; newsgroup; unmoderatednewsgroup.AMD See Advanced Micro Devices, Inc.American National StandardsInstitute AbbreviatedANSI.Anonprofitorganization of more than 1000 businessand industry groups, founded in 1918,devoted to the development of voluntarystandards.ANSI represents the United States in the In-ternational Organization for Standardiza-tion (ISO) and is affiliated with CCITT.2461book Page 18 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 24. 19analogANSI committees have developed many im-portant standards, including the following:IANSI X3J11: Standard for the C pro-gramming language, including languagesemantics, syntax, execution environ-ment, and the definition of the library andheader files.IANSI X3J16: Standard for the C++ pro-gramming language.IANSI X3J3: Definition of the Fortran pro-gramming language compiler.IANSI X3.131-1986: Definition of theSCSI standard. The X3T9.2 standard con-tains the extensions for SCSI-2.IANSI X3T9.5: The working group for theFDDI definition.American Standard Code for Informa-tion Interchange Abbreviated ASCII,pronounced “as-kee.” A standard codingscheme that assigns numeric values to let-ters, numbers, punctuation characters, andcontrol characters to achieve compatibilityamong different computers and peripheraldevices. In ASCII, each character is repre-sented by a unique integer value in the range0 through 255. See Appendix C.See also ASCII extended character set;ASCII file; ASCII standard character set;double-byte character set; ExtendedBinary Coded Decimal Interchange Code;Unicode.American Wire Gauge AbbreviatedAWG. A measurement system that specifiescopper wire by thickness; as thicknessincreases, the AWG number decreases.Some common conductor gauges are:IRS-232-C: 22 or 24 AWGIThick Ethernet: 12 AWGIThin Ethernet: 20 AWGSee also cabling standards; EIA/TIA 586;Type 1–9 cable.America Online, Inc. AbbreviatedAOL. The world’s largest online service,headquartered in Vienna, Virginia, withmore than 15 million subscribers. AOLprovides a gateway to the Internet, as wellas its own news, sports, e-mail, chat rooms,and other fee-based services. In 1997, AOLbought CompuServe, and in 1998,Netscape Communications.For more information about America On-line, see (&) 1. In Unix, a commandsuffix used to indicate that the precedingcommand should be run in the background.2. In Unix, a root user command used tostart a daemon that is to keep running afterlogout.3. In HTML, a special character entry in adocument.See also daemon; HyperText MarkupLanguage.AMPS See Advanced Mobile PhoneService.analog Describes any device that repre-sents changing values by a continuouslyvariable physical property, such as a volt-age in a circuit. Analog often refers to trans-mission methods developed to transmitvoice signals rather than high-speed digitalsignals.2461book Page 19 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 25. Andrews File System20Andrews File System AbbreviatedAFS. A protocol developed at CarnegieMellon University; used to share remotefiles across systems using TCP/IP.AFS has certain advantages over NFS inthat it only allows users to access fileslinked to AFS rather than giving access toall files, it has a built-in cache that helps toreduce the demands made on the system,and system administrators can allocate diskspace on the fly as required.See also Distributed File System; NetworkFile System; Transmission Control Proto-col/Internet Protocol.angle brackets The less-than (<) andgreater-than (>) symbols used to identify atag in an HTML document.Also used to identify the return address inan e-mail message header.See also HyperText MarkupLanguage; tag.ANI See automatic numberidentification.anonymous FTP A method used to ac-cess an Internet computer that does not re-quire you to have an account on the targetcomputer system. Simply log on to the In-ternet computer with the user name anon-ymous, and use your e-mail address as yourpassword. This access method was original-ly provided as a courtesy so that system ad-ministrators could see who had logged onto their systems, but now it is often requiredto gain access to an Internet computer thathas FTP service.You cannot use anonymous FTP with everycomputer on the Internet, only with thosesystems set up to offer the service. The sys-tem administrator decides which files anddirectories will be open to public access,and the rest of the system is considered offlimits and cannot be accessed by anony-mous FTP users. Some sites only allow youto download files; as a security precaution,you are not allowed to upload files.See also File Transfer Protocol; Telnet.anonymous posting In a Usenet news-group, a public message posted via an anon-ymous server in order to conceal theidentity of the original sender.anonymous remailer See anonymousserver.anonymous server A special Usenetservice that removes from a Usenet post allheader information that could identify theoriginal sender and then forwards the mes-sage to its final destination. If you use ananonymous server, be sure to remove yoursignature from the end of the message; notall anonymous servers look for and thenstrip a signature. Also known as an anony-mous remailer.ANSI SeeAmericanNationalStandardsInstitute.answer mode A function that allows amodem to answer an incoming call, detectthe protocol being used by the calling mo-dem, and synchronize with that protocol.See also auto-answer; auto-dial.2461book Page 20 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 26. 21Apple Computer, Inc.antivirus program A program that de-tects or eliminates a computer virus. Someantivirus programs can detect suspiciousactivity on your computer as it happens;others must be run periodically as part ofyour normal housekeeping activities.An antivirus program locates and identifiesa virus by looking for characteristic pat-terns or suspicious activity in the system,such as unexpected disk access or .EXE fileschanging in some unusual way. It recogniz-es the virus by comparing information fromthe system against a database of known vi-ruses, which is kept on disk.Be sure you test an antivirus program care-fully on your network before you employit everywhere; some programs impose anenormous overhead on normal networkoperations.See also file-infecting virus; macro virus;multipart virus; polymorphic virus; stealthvirus; Trojan Horse; vaccine; virus.AnyNet A family of gateway productsfrom IBM used to integrate SNA, TCP/IP,and NetBIOS networks with products run-ning on IBM’s AIX/6000, OS/2, and OS/400 and with Microsoft Windows.AOL See America Online, Inc.Apache HTTP Server A freeware Webserver, supported by the Unix community,in use on almost half of the Web sites on theInternet. So called because the original uni-versity-lab software was patched with newfeatures and fixes until it became known as“a patchy server.”Apache dominates the Web because of itslow cost, excellent performance, good scal-ability, and great flexibility. Don’t expecteasy graphical configuration programs andhypertext help; you’ll get the command lineand the man pages instead, so it certainlyhelps to have staff with Unix experience.Apache Server is available as part of the RedHat Software Linux distribution, whichalso provides developers with full supportfor CGI, Perl, Tcl, a C or C++ compiler, anApache server API, and a SQL database.For more information on Apache Server,see The Apache Group Web site also Linux; Red Hat Software.API See application programminginterface.APM See Advanced See application.APPC See Advanced Program-to-Pro-gram Communications.APPI See Advanced Peer-to-Peer Inter-networking.Apple Computer, Inc. Manufacturer ofthe successful Macintosh and Quadra seriesof computers based on Motorola chips. Thecompany was founded by Steve Wozniakand Steve Jobs in a garage on April 1, 1976.In 1993, Apple entered the consumer elec-tronics marketplace with a personal digitalassistant known as Newton, combiningfax, electronic mail, and other functionsinto a unit small enough to fit into a pocket.2461book Page 21 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 27. Apple Desktop Bus22In 1994, Apple launched a new series ofcomputers called the Power Macintosh (orPower Mac), based on the PowerPC, capa-ble of running either the Macintosh operat-ing system or Windows programs undersoftware emulation.Apple always kept the architecture of theMac proprietary, a move that has cost thecompany considerable market share; never-theless, Apple has always had a strong fol-lowing among musicians and graphicaldesigners.In 1997, Steve Jobs rejoined Apple and, af-ter realigning Apple’s product line, led thedevelopment and launch of the popular andcapable Internet-ready iMac computer.For more information on Apple Computer,Inc., see Desktop Bus A serial communi-cations link that connects low-speed inputdevices, such as a mouse or a keyboard, tothe computer on the Macintosh SE, II, IIx,IIcx, and SE/30.Light pens, trackballs, and drawing tabletsmay also be connected via the Apple Desk-top Bus. Most Apple Desktop Bus devicesallow one device to be daisy-chained to thenext, up to a maximum of 16 devices.Apple Macintosh See Macintosh.AppleShare Network software fromApple Computer that requires a dedicatedMacintosh computer acting as a central-ized server and includes both server andworkstation software. AppleShare uses theAppleTalk Filing Protocol (AFP).AppleTalk AnAppleMacintoshnetworkprotocol, based on the OSI Reference Mod-el, which gives every Macintosh network-ing capabilities. AppleTalk can run underseveral network operating systems, includ-ing Apple Computer’s AppleShare, NovellNetWare for the Macintosh, and TOPSfrom Sun Microsystems.AppleTalk includes specifications for thedata-link layer as LocalTalk, EtherTalk,FDDI-Talk, or TokenTalk, and the networklayer as Datagram Delivery Protocol. Thetransport layer contains four protocols:IRouting Table Maintenance Protocol(RTMP)IAppleTalk Echo Protocol (AEP)IAppleTalk Transaction Protocol (ATP)IName Binding Protocol (NBP)The session layer includesIAppleTalk Data Stream Protocol (ADSP)IAppleTalk Session Protocol (ASP)IPrinter Access Protocol (PAP)IZone Information Protocol (ZIP)The presentation layer adds the AppleTalkFiling Protocol (AFP) for access to remotefiles on shared disks.AppleTalk Filing Protocol Abbreviat-ed AFP. AFP is located in the presentationand application layers of the AppleTalkprotocol stack. AFP lets users access remotefiles as though they were local, as well asproviding security features that can restrictuser access to certain files.2461book Page 22 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 28. 23applicationAPPLETALK PROTOCOL STACKapplication Abbreviated app, or if theapplication is a small one, it is referred to asan applet. A computer program designed toperform a specific task, such as accounting,scientific analysis, word processing, ordesktop publishing.In general, applications can be distinguishedfrom system software, system utilities, andcomputer language compilers, and they canbe categorized as either stand-alone ornetwork applications. Stand-alone applica-tions run from the hard disk in an indepen-dentcomputer,soonlyoneuseratatimecanaccess the application. Network applica-tions run on networked computers and canbe shared by many users. Advanced applica-tions such as groupware and e-mail allowcommunications between network users.See also application metering; client/server architecture; LAN-aware.2461book Page 23 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 29. Application Binary Interface24Application Binary Interface Abbrevi-ated ABI. A specification that aims to ensurebinary compatibility between applicationsrunning on the same family of processors orCPUs using Unix System V Release 4.Applications developed using ABI can runon hardware from different manufacturerswithout being recompiled; any system callsneeded for specific hardware are main-tained in libraries.The specification was originally developedby AT&T and Sun Microsystems and in-cludes a test and verification suite used todetermine if a system complies with thestandard.See also application programminginterface.application layer The seventh, or high-est, layer in the OSI Reference Model forcomputer-to-computer communications.This layer uses services provided by thelower layers but is completely insulatedfrom the details of the network hardware. Itdescribes how applications interact withthe network operating system, includingdatabase management, electronic mail, andterminal emulation programs.See also OSI Reference Model.application-level filter A category offirewall that provides a high degree of secu-rity but at the cost of lower speed and great-er complexity. Typical application-levelfilters can provide proxy services for appli-cations and protocols such as Telnet, FTP,HTTP, and SMTP.See also firewall; packet-level filter; state-less filter.application log In Microsoft Windows2000, a system log that contains events gen-erated by applications or by alert logs. Youcan use the Event Viewer to display the con-tents of the application log.See also Event Viewer; security log; sys-tem log.application metering The process ofcounting the number of executions of thecopies of an application in use on the net-work at any given time and ensuring thatthe number does not exceed preset limits.Application metering is usually performedby a network management application run-ning on the file server. Most applicationmetering software will allow only a certainnumber of copies (usually that numberspecified in the application software li-cense) of an application to run at any onetime and will send a message to any userswho try to exceed this limit.See also concurrent license.Application object In Novell DirectoryServices (NDS), a leaf object that representsa network application in a NetWare Direc-tory tree.See also Computer object; container ob-ject; leaf object; Novell Directory Services.application programming interfaceAbbreviated API. The complete set of alloperating system functions that an applica-tion can use to perform such tasks as man-aging files and displaying information.An API provides a standard way to write anapplication, and it also describes how theapplication should use the functions it pro-vides. Using an API is quicker and easier2461book Page 24 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 30. 25archive filethan developing functions from scratch andhelps to ensure some level of consistencyamong all the applications developed for aspecific operating system.In operating systems that support a graphi-cal user interface, the API also defines func-tionstosupportwindows,icons,drop-downmenus, and other components of the inter-face. In network operating systems, an APIdefines a standard method that applicationscan use to take advantage of all the networkfeatures.application server A special-purposefile server that is optimized for a specifictask, such as communications or a databaseapplication, and that uses higher-end hard-ware than a typical file server.See also superserver.application-specific integratedcircuit Abbreviated ASIC. A computerchip developed for a specific purpose, de-signed by incorporating standard cells froma library rather than created from scratch.Also known as gate arrays, ASICs are foundin all sorts of appliances, including mo-dems,securitysystems,digitalcameras,andeven microwave ovens and automobiles.APPN See Advanced Peer-to-Peer Net-working.ARB See Area Border router.arbitration The set of rules used to man-age competing demands for a computerresource, such as memory or peripheral de-vices, made by multiple processes or users.See also contention.Archie A system used on the Internet tolocate files available by anonymous FTP.Once a week, special programs connect toall the known anonymous FTP sites on theInternet and collect a complete listing of allthe publicly available files. This listing offiles is kept in an Internet Archive Database,and when you ask Archie to look for a file,it searches this database rather than thewhole Internet; you then use anonymousFTP to retrieve the file.See also anonymous FTP.architecture 1. The overall design andconstruction of all or part of a computer,particularlytheprocessorhardwareandthesize and ordering sequence of its bytes.2. Theoveralldesignofsoftware,includinginterfaces to other software, the operatingsystem, and to the network.See also client/server architecture; closedarchitecture; complex instruction set com-puting; open architecture; reduced instruc-tion set computing.archive 1. To transfer files to some formof long-term storage, such as magnetic tapeor large-capacity disk, when the files are nolonger needed regularly but must be main-tained for periodic reference.2. On the Internet, a site containing acollection of files available via anonymousFTP.3. A compressed file.archive file A single file that contains oneor more files or directories that may havebeen compressed to save space. Archives areoften used as a way to transport large num-bers of related files across the Internet.2461book Page 25 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 31. ARCNet26An archive file created under Unix may havethe filename extension .TAR (for tape ar-chive), .GZ (for gzip), or .Z (for compress orpack). Those created in Windows may havethe filename extension .ZIP from the PKZIPor WinZip programs. Archive files createdon a Macintosh will have the filename exten-sion .SAE or .SIT from the StuffIt program.An Internet host that provides access tolarge numbers of archive files is known asan archive site.ARCNet Acronym for Attached Resourc-es Computing Network. A network avail-able from the Datapoint Corporation andother vendors that can connect a wide vari-ety of PCs and workstations (up to a maxi-mum of 255) on coaxial, twisted-pair, orfiber-optic cable. ARCnet uses a proprietarytoken-passing access method at speeds of2.5Mbps. ARCNet Plus is Datapoint’s pro-prietary product that runs at 20Mbps.ARCNetwaspopularforsmallernetworks,because it is relatively easy to set up and tooperate and also because the componentsare inexpensive and widely available. Thesedays, however, it is showing its age and isno longer sold by the major vendors.See also Token Ring network.Area Border router Abbreviated ARB.In an internetwork that uses link state rout-ing protocols such as Open Shortest PathFirst (OSPF) protocols, a router that has atleast one connection to another router in adifferent part of the internetwork. Alsoknown as a Border router.See also Autonomous System Borderrouter; Open Shortest Path First.ARIS See Aggregate Route-Based IPSwitching.ARLL See advanced run-length limitedencoding.ARP See Address Resolution Protocol.ARPAnet Acronym for Advanced Re-search Projects Agency Network. A re-search network funded by the DefenseAdvanced Research Projects Agency(DARPA) to link universities and govern-ment research agencies, originally built byBBN, Inc., in 1969. It was the backbonefor the now huge Internet. TCP/IP proto-cols were pioneered on ARPAnet. In 1983,the military communications portion wassplit off into the MILnet.article An e-mail message posted to oneof the Usenet newsgroups, accessible byanyone with a newsreader and a connectionto the Internet. Also called a post.See also newsreader.AS/400 A series of mid-range mini-computers from IBM, first introduced in1988, that replaces the System/36 and Sys-tem/38 series of computers. The AS/400can serve in a wide variety of network con-figurations: as a host or an intermediatenode to other AS/400 and System/3x com-puters, as a remote system to System/370-controlled networks, or as a network serv-er to a group of PCs.ASBR See Autonomous System Bor-der router.Ascend Certified Technical ExpertAbbreviated ACTE. A certification schemefrom Ascend Communications, Inc., aimed2461book Page 26 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 32. 27ASPat technical professionals with experiencein installing, configuring, and trouble-shooting Ascend remote-access products.Two written exams, the Networking andTelecommunications exam, and the Re-mote Access exam, are followed by a hands-on lab test administered at Ascend’s head-quarters in Alameda, CA.Ascend Communications, Inc. A lead-ing provider of solutions for telecommuni-cations carriers, ISPs, and corporatecustomers, Ascend manufactures productsfor remote access, for wide area network-ing, and for linking telephone switches, net-work connections, and videoconferencingfacilities to phone company networks.Ascend recently acquired Cascade Commu-nications, establishing the company as oneof the largest suppliers of frame-relay andATM equipment. In 1999, Ascend wasbought by Lucent Technologies.For more information on Ascend, See American Standard Code forInformation Interchange.ASCII extended character set The sec-ond group of characters, from 128 through255, in the ASCII character set. The extend-ed ASCII character set is assigned variablesets of characters by computer hardwaremanufacturersandsoftwaredevelopers,andit is not necessarily compatible between dif-ferent computers. The IBM extended char-acter set used in the PC (see Appendix C)includes mathematics symbols and charac-ters from the PC line-drawing set.See also American Standard Code for In-formation Interchange; ASCII file; ASCIIstandard character set; double-byte char-acter set; Extended Binary Coded DecimalInterchange Code; Unicode.ASCII file A file that contains only textcharacters from the ASCII character set. AnASCII file can include letters, numbers, andpunctuation symbols, but does not containany hidden text-formatting codes. Alsoknown as a text file or an ASCII text file.See also American Standard Code for In-formation Interchange; ASCII extendedcharacterset;ASCIIstandardcharacterset;binary file.ASCII standard character set A char-acter set that consists of the first 128 (from0 through 127) ASCII characters. The val-ues 0 through 31 are used for nonprintingcontrol codes (see Appendix C), and therange 32 through 127 is used to representthe letters of the alphabet and commonpunctuation symbols. The entire set from 0through 127 is referred to as the standardASCII character set. All computers that useASCII can understand the standard ASCIIcharacter set.See also American Standard Code for In-formation Interchange; ASCII file; ASCII ex-tended character set; double-bytecharacter set; Extended Binary Coded Dec-imal Interchange Code; Unicode.ASCII text file See ASCII file.ASE See Accredited Systems Engineer.ASIC See application-specificintegrated circuit.ASP See Active Server Pages.2461book Page 27 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 33. assembly language28assembly language A low-level pro-gramming language in which each programstatement must correspond to a single ma-chine language instruction that the proces-sor can execute.Assembly languages are specific to a givenmicroprocessor and, as such, are not porta-ble; programs written for one type of pro-cessor must be rewritten before they can beused on another type of processor.You use assembly language for two reasons:ITo wring as much performance out of theprocessor as possibleITo gain access to specific characteristicsof the hardware that might not be possiblefrom a higher-level languageSee also compiler; interpreter; machinelanguage; microcodeAssociate Business ContinuityProfessional Abbreviated ABCP. A cer-tification from Disaster Recovery InstituteInternational (DRII) that covers basic in-formation on business continuity planningand disaster recovery.See also Certified Business ContinuityProfessional; Master Business Continu-ity Professional.Associated Accredited SystemsEngineer Abbreviated AASE. A certifica-tionfromCompaqdesignedtoevaluateandrecognize basic knowledge of PC architec-ture and operations. An AASE may choosetospecializeinMicrosoftWindows2000orNovell NetWare operation.See also Accredited Systems Engineer.Association of Banyan UsersInternational Abbreviated ABUI. TheBanyan user group, with 1700 membersworldwide, concerned with all hardwareand software related to the Banyan system,including Banyan VINES.See also Banyan VINES.asterisk In several operating systems,you can use the asterisk (*) as a wildcardcharacter to represent one or more un-known characters in a filename or filenameextension.See also question mark; star-dot-star.AST Research One of the world’s topten computer manufacturers, AST Re-search makes desktop, laptop, notebook,and hand-held computers, as well as moni-tors, graphics cards, and memory products.A subsidiary of Samsung Electronics Com-pany Limited.FormoreinformationonASTResearch, multiprocessing A mul-tiprocessing design in which the program-mer matches a specific task to a certainprocessor when writing the program.This design makes for a much less flexiblesystem than SMP (symmetrical multipro-cessing) and may result in one processor be-ing overworked while another stands idle.SMP allocates tasks to processors as theprogram starts up, on the basis of currentsystem load and available resources. Need-less to say, asymmetrical multiprocessingsystems are easier to design, code, and testthan symmetrical multiprocessing systems.2461book Page 28 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 34. 29asynchronous transmissionAsymmetric Digital Subscriber LineAbbreviated ADSL. A high-speed datatransmission technology originally devel-oped by Bellcore and now standardized byANSI as T1.413. ADSL delivers high band-width over existing twisted-pair coppertelephone lines. Also called AsymmetricDigital Subscriber Loop.ADSL supports speeds in the range of 1.5 to9Mbps in the downstream direction (fromthe network to the subscriber) and supportsupstream speeds in the range of 16 Kbps to640 Kbps; hence, the term asymmetric.See also Digital Subscriber Line; High-Bit-Rate Digital Subscriber Line; Rate-AdaptiveDigital Subscriber Line; Single-Line Digi-tal Subscriber Line; Very-High-Bit-RateDigital Subscriber Line.Assymetric Digital Subscriber LoopSee Assymetric Digital Subscriber Line.asynchronous communications Seeasynchronous transmission.asynchronous communicationsserver A LAN server that allows a net-work user to dial out of the network intothe public switched telephone system or toaccess leased lines for asynchronous com-munications. Asynchronous communica-tions servers may also be called dial-in/dial-out servers or modem servers.asynchronous time-divisionmultiplexing Abbreviated ATDM. Anasynchronous and adaptive version of time-division multiplexing in which time slots areallocated dynamically based on demand.See also time-division multiplexing.Asynchronous Transfer Mode Abbre-viated ATM. A method used for transmit-ting voice, video, and data over high-speedLANs and WANs. ATM uses continuousbursts of fixed-length packets called cells totransmit data. The basic packet consists of53 bytes, 5 of which are used for controlfunctions and 48 for data.ATM is a connection-oriented protocol,and two kinds of connections are possible:IPermanent virtual circuits (PVCs), inwhich connections are created manuallyISwitched virtual circuits (SVCs), in whichconnections are made automaticallySpeeds of up to 2.488Gbps have beenachieved in testing. ATM will find wide ac-ceptance in the LAN and WAN arenas as asolution to integrating disparate networksover large geographical distances. Alsoknown as cell relay.See also permanent virtual circuit;switched virtual circuit.asynchronous transmission Amethodof data transmission that uses start bits andstop bits to coordinate the flow of data sothat the time intervals between individualcharacters do not need to be equal. Parityalso may be used to check the accuracy ofthe data received.See also communications parameters;data bits; synchronous transmission.2461book Page 29 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 35. ATA30ASYNCHRONOUS TRANSMISSIONATA See Advanced TechnologyAttachment.AT command set A set of standard in-structions used to activate features on a mo-dem. Originally developed by HayesMicrocomputer Products, the AT com-mand set is now used by almost all modemmanufacturers.See also modem.ATDM See asynchronous time-divisionmultiplexing.ATG See address translation gateway.ATM See Asynchronous Transfer Mode.ATM25 A low-cost version of Asynchro-nous Transfer Mode (ATM) that runs onCategory 3 unshielded twisted-pair cableand provides 25Mbps transmissions inboth directions.See also Asynchronous Transfer Mode; IPover ATM; LAN Emulation; Multiprotocolover ATM.ATM Adaptation Layer AbbreviatedAAL. A service-dependent layer in Asyn-chronous Transfer Mode (ATM) that pro-vides the protocol translation betweenATM and the other communications servic-es involved in a transmission.AAL has several service types and classes ofoperation to handle different kinds of traf-fic, depending on how data is transmitted,the bandwidth required, and the types ofconnection involved.See also convergence sublayer; segmen-tation and reassembly sublayer.ATM LAN Emulation An Asynchro-nous Transfer Mode (ATM) variation thatuses software to make the network operat-ing system see an ATM adapter as an Ether-net or Token Ring adapter.See also IP over ATM; LAN Emulation;Multiprotocol over ATM.2461book Page 30 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 36. 31AUDITCONat symbol The separating character (@)betweenaccountnameanddomainnameinan Internet e-mail address.See also bang path.AT&T The parent company of Bell Labo-ratories, the original developers of Unix.For many years Bell Labs was one of thetwo major development centers for Unix(the other being the Computer Systems Re-search Group at the University of Califor-nia at Berkeley), but in 1990, AT&Tformed Unix Systems Laboratories, or USL,to continue the development of Unix. In1993, USL was sold to Novell, and in 1995,Novell sold the rights to SCO (Santa CruzOperation).See also Baby Bells; Regional Bell Operat-ing Companies.attach To establish a connection be-tween a workstation and a network fileserver; particularly, to access additionalservers after logging on to one server.attachment See enclosure.Attachment Unit Interface Abbreviat-ed AUI. A 15-pin socket used by someEthernet devices. AUI connections adaptbetween two different cabling types andwork with a wide range of wiring schemes.Also known as a DIX (for Digital, Intel,Xerox) connector.attack An attempt to circumvent the se-curity measures in place on a network eitherto gain unauthorized access to the system orto force a denial of service.See also brute-force attack; dictionary at-tack; social engineering.attenuation The decrease in power of asignal with increasing distance. Attenua-tion is measured in decibels, and it increasesas the power of the signal decreases. Thebest cables (those exhibiting the least atten-uation) are fiber-optic lines, and the worstcables are unshielded, untwisted-pair lines,such as the silver, flat-satin cables used inshort-run telephone and modem lines.In a LAN, attenuation can become a prob-lem when cable lengths exceed the statednetwork specification; however, the usefullength of a cable may be extended by the useof a repeater.attribute 1. A file attribute is a tech-nique for describing access to and proper-ties of files and directories within a filesystem. You may see the termattribute usedinterchangeably with the term property.2. A screen attribute controls a character’sbackground and foreground colors, as wellas other characteristics, such as underlining,reverse video, and blinking or animation.3. In operating systems, a characteristicthat indicates whether a file is a read-onlyfile, a hidden file, or a system file or haschanged in some way since it was lastbacked up.4. InmarkuplanguagessuchasHTMLandSGML, a name-value pair within a taggedelement that modifies certain characteris-tics of that element.5. In a database record, the name or struc-ture of a field.See also tag.AUDITCON A Novell NetWare and In-tranetWare workstation utility that creates2461book Page 31 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 37. audit policy32a log file to allow an independent auditor toverify that network transactions are accu-rate and that confidential information is se-cure. When auditing is enabled, an auditorcan track when files or directories are cre-ated, deleted, modified, salvaged, moved,or renamed. Changes to security rights canalso be tracked.audit policy In Microsoft Windows2000, the policy that defines the securityevents to track and report to the networkadministrator.See also security log.audit trail An automatic feature of cer-tain programs or operating systems thatcreates a running record of all transactions.An audit trail allows you to track a piece ofdata from the moment it enters the systemto the moment it leaves and to determinethe origin of any changes to that data.auditing The process of scrutinizing net-work security-related events and transac-tions to ensure that they are accurate,particularly reviewing attempts to create,access, and delete files and directories andreviewing security violations. Records ofthese events are usually stored in a securitylog file, which can only be examined by us-ers with special permissions.AUI See Attachment Unit Interface.authentication In a network operatingsystem or multiuser system, the process thatvalidates a user’s logon information.Authentication may involve comparing theuser name and password to a list of autho-rized users. If a match is found, the user canlog on and access the system in accordancewith the rights or permissions assigned tohis or her user account.See also authorization; Kerberos; pass-word; user; user account.authoring The process of preparing amultimedia presentation or a Web page.This involves not only writing the text ofthe presentation or Web page, but also theproduction of the slides, sound, video, andgraphical components.authorization The provision of rights orpermissions based on identity. Authoriza-tion and authentication go hand in hand innetworking; your access to services is basedon your identity, and the authenticationprocesses confirm that you are who you sayyou are.See also A feature of a modemthat allows it to answer incoming callsautomatically.See also answer mode; dialback A feature of a modem that al-lows it to open a telephone line and start acall. To auto-dial, the modem sends a seriesof pulses or tones that represent a storedtelephone number.See also callback modem.AUTOEXEC.BAT A contraction of Au-tomatically Executed Batch. A specialMS-DOS batch file, located in the root di-rectory of the startup disk, that runs auto-matically every time you start or restartyour computer. The commands contained2461book Page 32 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 38. 33Available Cell Ratein AUTOEXEC.BAT are executed one byone, just as if you typed them at the systemprompt. An AUTOEXEC.BAT file can beused to load hardware device drivers, setthe system prompt, change the defaultdrive to the first network drive, and log theuser in to the file server.In OS/2, you can select any batch file to beused as AUTOEXEC.BAT for a specificMS-DOS session, so you can tailor specificenvironments for separate MS-DOS sessions,each using a different AUTOEXEC.BAT file.SeealsoAUTOEXEC.NCF;boot;bootstrap;CONFIG.SYS.AUTOEXEC.NCF A Novell NetWarebatch file usually located on the NetWarepartition of the server’s hard disk, used toset the NetWare operating system configu-ration. AUTOEXEC.NCF loads the LANdrivers, the NLMs, and the settings for thenetwork interface boards and then bindsthe protocols to the installed drivers.Automatic Client Upgrade A mecha-nismusedtoupgradeNovellclientsoftwareduring the logon process by executing fourseparate programs called by the logonscript. Automatic Client Upgrade can bevery useful when all client workstations usestandard configurations.automatic forwarding A feature ofmany e-mail programs that automaticallyretransmits incoming messages to anothere-mail address.automatic number identification Ab-breviated ANI. A method of passing a call-er’s telephone number over the network tothe recipient so that the caller can be iden-tified. ANI is often associated with ISDNand is sometimes known as caller ID.automatic rollback In a Novell Net-Ware network, a feature of the TransactionTracking System (TTS) that abandons thecurrent transaction and returns a databaseto its original condition if the network failsin the middle of a transaction. Automaticrollback prevents the database from beingcorrupted by information from incompletetransactions.See also backing out.Autonomous System Border routerAbbreviated ASBR. In an internetwork thatuses link state routing protocols such asOpen Shortest Path First (OSPF) protocols,a router that has at least one connectionto a router in an external network.See also Area Border router; Open Short-est Path First.AutoPlay A feature of Microsoft Win-dows that automatically executes an appli-cation from a CD-ROM or automaticallyplays an audio CD when the disk is insertedinto the CD-ROM drive.Available Bit Rate A Type 3 or Type 4Asynchronous Transfer Mode AdaptionLayer (AAL) service designed for non–time-criticalapplicationssuchasLANemulationand LAN internetworking.See also Constant Bit Rate; Unspecified BitRate; Variable Bit Rate.Available Cell Rate Abbreviated ACR.A measure of the bandwidth in Asynchro-nous Transfer Mode (ATM) networks. TheACR value represents the number of ATM2461book Page 33 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 39. avatar34cells available or allowed per second for aspecific quality of service (QoS) class.Available Cell Rate is also known as Al-lowed Cell Rate.See also Asynchronous Transfer Mode;Minimum Cell Rate; Peak Cell Rate; Sus-tainable Cell Rate.avatar 1. In Unix, another name for thesuperuser account; an alternative to thename root.2. A visual representation of a user in ashared virtual-reality environment.AWG See American Wire Gauge.2461book Page 34 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 40. 35back-end systemBBaan Advanced Certification Abbrevi-ated BAC. A certification from Baan avail-able in four specialties covering the BaanIV suite of products: Enterprise Logistics,Enterprise Finance, Enterprise Tools,and Enterprise Modeler.See also Baan Basic Certification.Baan Basic Certification AbbreviatedBBC. A certification from Baan designed toevaluate basic proficiency with the Baan IVsuite of products; a prerequisite qualifica-tion to taking the Baan Advanced Certifica-tion exams.See also Baan Advanced Certification.Baan Company A leading provider ofenterprise and inter-enterprise businesssoftware used for managing finance, man-ufacturing, inventory, distribution, trans-portation, and administrative functions forlarge companies.For more information on Baan, Bells A slang term for the 22 Re-gional Bell Operating Companies (RBOC),formed when AT&T was broken up in 1984.See also Bell Labs.BAC See Baan Advanced Certification.backbone That portion of the networkthat manages the bulk of the traffic. Thebackbone may connect several locations orbuildings, and other, smaller networks maybe attached to it. The backbone often usesa higher-speed protocol than the individualLAN segments.back-end processor A secondary pro-cessor that performs one specialized taskvery effectively, freeing the main processorfor other, more important work.back-end system The server part of aclient/server system that runs on one ormore file servers and provides services tothe front-end applications running on net-workedworkstations.Theback-endsystemaccepts query requests sent from a front-end application, processes those requests,and returns the results to the workstation.Back-end systems may be PC-based serv-ers, superservers, midrange systems, ormainframes.See also client/server architecture.2461book Page 35 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 41. background36BACKBONEbackground 1. On a computer screen,thecoloronwhichcharactersaredisplayed;for example, white characters may appearon a blue background.2. In an operating system, a process thatruns in the background generally runs at alower level of priority than a foregroundtask and does not accept input from the us-er. Only multitasking operating systemssupport true background and foregroundprocessing, but some applications can mim-ic it. For example, many word processorscan print a document while still acceptinginput from the keyboard. In older systems,a process spends its entire existence in eitherthebackgroundortheforeground;innewersystems, you can change the processing en-vironment and move foreground programsinto the background, and vice versa.See also ampersand; foreground;multitasking.background authentication The pro-cess used to give a workstation access to aparticular server. For example, in Novell2461book Page 36 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 42. 37backupNetWare, password authentication uses apublic key encryption scheme to protectpassword information before it is transmit-ted over the network. All this activity takesplace in the background, and all the userhas to do is enter his or her password.background noise Any unwanted sig-nal that enters a line, channel, or circuit; forexample, electrical interference on a tele-phone circuit.See also noise.backing out The process of abandoningthe current transaction and returning a da-tabase to its original condition if the net-work fails during the transaction. Thisprocess prevents the database from beingcorrupted by information from the incom-plete transaction.See also automatic rollback; TransactionTracking System.backlink In Novell Directory Services, anattribute used by a directory to indicate theexternal references to a property.backslash 1. In MS-DOS, OS/2, andother operating systems, you must use thebackslash character () to separate directoryor subdirectory names in a path statementor when changing to another directory.2. A shorthand name for the root directory.Sometimes called the reverse slash orbackslant.See also slash.backup An up-to-date copy of all yourfiles. You make a backup for several reasons:IInsurance against possible hard-disk orfile-server failure. Hard disks often failcompletely, taking all your work withthem. If this failure occurs, you can reloadyour files and directories from the backupcopy. A backup is your insurance againstdisk failure affecting the thousands orpossibly tens of thousands of files youmight have on your file server.IProtection against accidental deletion offiles or directories. Again, if you mistak-enly delete a file or directory, you can re-trieve a copy from your last backup.IProtection against the new version of soft-ware you are about to install not workingto your expectations; make a backup be-fore installing new software.IAs an archive at the end of a project, whena person leaves your company, or at theend of a financial period such as year-endclose.Your decision when or how often to makea backup depends on how frequently im-portant data on your system changes. If yourely on certain files always being availableon your system, it is crucial that you makeregular, consistent backups. Here are somebackup tips:IKeep multiple copies; redundancy shouldbe a part of your backup plan.ITest your backups to make sure they arewhat you think they are before you bringthe server into service, and make sure youcan reload the information you need.IStore your backups in a secure off-site lo-cation; do not leave them right next to thecomputer (if the computer is damaged byan accident, the backup may be damagedas well).IReplace your backup media on a regularbasis.2461book Page 37 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 43. backup browser38IConsider making incremental backups ofcritical data at more frequent intervals.It all comes down to one very simple rule:back up all the files that you cannot affordto lose. Do it now.See also archive; differential backup; diskduplexing; disk mirroring; full backup; in-cremental backup.backup browser InMicrosoftWindows2000 Server, a computer that maintains alist of computers and services available onthe network. This list is provided by themaster browser and distributed to a work-group or a domain by the backup browser.See also browser; master browser.backup domain controller In Micro-soft Windows NT, a server containing ac-curate replications of the security and userdatabases.The backup domain controller receives acopy of the domain’s directory database,containing all the account and security infor-mation for the domain, from the primary do-main controller. This copy is periodicallysynchronized with the original master data-base. A domain can contain several backupdomain controllers.See also domain controller; primary do-main controller.backup program An application thatyou use to make archive or backup copies ofimportant data files.Most operating systems offer commandsfor making backups, but many are limitedin capability. The most cost-effective back-up programs are from third-party vendors.Seealsodiskduplexing;diskmirroring;fullbackup; incremental backup; tape car-tridge; tape drive.backward compatibility Full compati-bility with earlier versions of the same ap-plication or computer system.Backward Error Correction Abbreviat-ed BEC. An error-correction method inwhich an error can be detected by the recip-ient, which immediately requests a retrans-mission of the affected data.See also error detection and correction.BACP See Bandwidth Allocation Con-trol Protocol.bad sector An area on a hard disk orfloppy disk that cannot be used to storedata because of a manufacturing defect oraccidental damage.The operating system will find, mark, andisolate bad sectors. Almost all hard diskshave some bad sectors, often listed in thebad track table. Usually, bad sectors are aresult of the manufacturing process and nota concern; the operating system will markthem as bad, and you will never even knowthey are there.bad track table A list of the defective ar-eas on a hard disk, usually determined dur-ing final testing of the disk at the factory.Some disk-preparation programs ask youto enter information from this list to reducethe time that a low-level format takes toprepare the disk for use by the operatingsystem.balun A contraction of balancedunbalanced. A small device used to connect2461book Page 38 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 44. 39Banyan VINESa balanced line (such as a twisted-paircable) to an unbalanced line (such as acoaxial cable). The balun matchesimpedances between the two media.bandwidth 1. In communications, thedifference between the highest and lowestfrequencies available for transmission inany given range.2. In networking, the transmission capaci-ty of a computer or a communicationschannel, stated in megabits per second(Mbps). For example, FDDI (Fiber Distrib-uted Data Interface) has a bandwidth of100Mbps. To relate this to a real-world ex-ample, a complete page of text, in English,is approximately 16,000 bits.Bandwidth Allocation ControlProtocol Abbreviated BACP. A pro-posedInternetprotocoldesignedtomanagea combination of dial-up links, usually overISDN connections.BACP provides bandwidth on demand andcan combine two or more circuits into a sin-gle circuit with a higher data rate.See also bandwidth on demand.bandwidth on demand A techniquethat allows the user to add additional band-width as the application requires it.Most network traffic does not flow in steadyand easily predictable streams, but in shortbursts, separated by longer periods of inac-tivity. This pattern makes it difficult to pre-dict peak loads. Bandwidth on demand isuseful for applications such as backups andvideoconferencingandallowstheusertopayfor only the amount of bandwidth used.See also virtual data network.bandwidth reservation A techniqueused to reserve channel capacity for specialtime-sensitive transmissions such asvideoconferencing and real-time audiotransmissions.bandwidth throttling AfeatureinsomeWeb server software that allows the systemadministrator to control or alter the pro-portions of bandwidth available to the ser-vices that the server provides.bang A name given in the Unix and Inter-net worlds to the exclamation point (!)character; also known aspling in the UnitedKingdom.See also bang path.bang path An old-style uucp e-mail ad-dress that uses exclamation points to sepa-rate the sequence of computer namesneeded to get to the addressee.Bang paths list addresses—general to spe-cific—from left to right, which is the reverseof the sequence used by other addressingschemes.See also at symbol; domain name; e-mailaddress; uucp.Banyan Systems, Inc. A leading pro-vider of enterprise network products, in-cluding the Banyan VINES networkoperating system, products based on theBanyan StreetTalk Directory, and Beyond-Mail messaging technologies.For more information on Banyan, VINES A network operating sys-tem from Banyan Systems. VINES (a con-traction of Virtual Networking Software) is2461book Page 39 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 45. Banyan VINES40based on a special version of the Unix Sys-tem V operating system.The following illustration shows the internalorganization of VINES. The Unix layer ishidden from view by VINES and is not avail-able for other applications. VINES providesall server functions, including those of a com-munications/modemserver,andoffersmanyoptions for connecting to minicomputers,mainframes, and other network file servers.VINES automatically manages protocolbinding and translations required betweenthe network interface cards for routing todifferent LAN segments. A complete set ofnetwork management tools is also available.Workstations can run MS-DOS, MicrosoftWindows, Unix, or OS/2, and they can storenative-form files on the server. Macintoshcomputers can also attach to the network.VINES offers special support for very largeLANs and WANs with multiple file servers.VINES also allows PCs that support multi-ple processors to use multiprocessing to di-vide the file-server processing load.See also Enterprise Network Services;StreetTalk.BANYAN VINES2461book Page 40 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 46. 41Basic Rate ISDNbase 10 radix See decimal.base64 An encoding scheme used byMIME-compliant mail systems to convertbinary files into a text format that can beprocessed and sent as e-mail.See also binary file; Multipurpose InternetMail Extension.baseband modem See line driver.baseband network A technique fortransmitting signals as direct-current pulsesratherthanasmodulatedsignals.Theentirebandwidth of the transmission medium isused by a single digital signal, so computersin a baseband network can transmit onlywhen the channel is not busy. However, thenetwork can use techniques such as multi-plexing to allow channel sharing.A baseband network can operate over rela-tively short distances (up to 2 miles if net-work traffic is light) at speeds from 50Kbpsto 100Mbps. Ethernet, AppleTalk, andmost PC local-area networks (LANs) usebaseband techniques.See also bandwidth; broadband network;frequency-divisionmultiplexing;statisticalmultiplexing; time-division multiplexing.baseline The process of determining anddocumenting network throughput and oth-er performance information when the net-work is operating under what is considereda normal load. Measured performancecharacteristics might include error-rateand data-transfer information, along withinformation about the most active usersand their applications.Bash In Unix, a popular command inter-preter. Bash, the Bourne-Again Shell, wasfirst released in 1989 by Brian Fox and ChetRamey, as part of the Free Software Foun-dation GNU Project.Bash provides features found in the otherUnix shells, particularly the Bourne shell,the C shell, and the Korn shell, and includesBourne shell syntax, redirection and quot-ing, C-shell command-line editing and tildeexpansion, job control, and command his-tory. Bash also includes built-in commandsand variables, as well as aliases from theKorn shell.See also Bourne shell; C shell; Korn shell;Linux; Unix shell.basic disk In Microsoft Windows 2000Server, a normal hard disk, available fromany operating system, that uses primaryand extended partitions to divide the avail-able space into logical units.See also dynamic disk.Basic Rate ISDN Abbreviated BRI. AnISDN service that offers two 64Kbps Bchannels used for data transfer and one16Kbps D channel used for signaling andcontrol information.Each B channel can carry a single digitalvoice call or can be used as a data channel;the B channels can also be combined into asingle 128Kbps data channel.See also 23B+D; 2B+D; Primary Rate ISDN.2461book Page 41 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 47. bastion host42BASIC RATE ISDNbastion host A computer system thatacts as the main connection to the Internetfor users of a LAN. A bastion host is usuallyconfigured in such a way as to minimize therisk of intruders gaining access to the mainLAN. It gets its name from the fortified pro-jections on the outer walls of medieval Eu-ropean castles.See also firewall; proxy server.batch file An ASCII file that containsoperating system commands and othercommands supported by the batch proces-sor. Batch files are used to automate repet-itive tasks. The commands in the file areexecuted one line at a time, just as if youhad typed them at the system prompt.baud A measurement of data-transmis-sion speed. Originally used in measuringthe speed of telegraph equipment, it nowusually refers to the data-transmissionspeed of a modem or other serial device.See also baud rate.baud rate In communications equip-ment, a measurement of the number of statechanges (from 0 to 1 or vice versa) per sec-ond on an asynchronous communicationschannel.Baud rate is often assumed to correspond tothe number of bits transmitted per second,but baud rate and bits per second (bps) arenot always the same. In high-speed digitalcommunications systems, one state changecan be made to represent more than onedata bit.See also baud; bits per second.Bay Networks Certified Expert A cer-tification from Bay Networks, Inc., de-signed to recognize technical expertise inconstructing enterprise-wide networkingsolutions. Currently, this certification isavailable in Router, Hub, and NetworkManagement technologies.Bay Networks Certified Specialist Acertification from Bay Networks, Inc., de-signed to evaluate a basic level of technicalexpertise in one or more Bay Networksproduct areas. Currently, this certificationis available in Router, Hub, Network Man-agement, Remote Access, and Switchingtechnologies.2461book Page 42 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 48. 43Berkeley Software Distribution UnixBay Networks, Inc. A leading manufac-turer of networking products such as hubs,routers, and switches, now venturing intothe areas of network management and vir-tual private networks. In 1998, the compa-ny announced a merger with NorthernTelecom.For more information on Bay Networks,see See Baan Basic Certification.BBS See bulletin board system.bcc See blind carbon copy.BCD See binary coded decimal.beaconing In a token-ring network, theprocess of informing other nodes that tokenpassing has been suspended because of a se-vere error condition, such as a broken cable.Communication cannot resume until thecondition is resolved.BEC See Backward Error Correction.Bell communications standards A setof data-transmission standards developedby AT&T in the 1980s that rapidly becamethe de facto standard for modem manufac-turers. Although several of these standardsare still widely used in the United States, theCCITT V series definitions are now gener-ally accepted as the defining standards formodem use, data compression, and associ-ated hardware.Bell Labs The research arm of AT&Tand the birthplace of the Unix operatingsystem and the C programming language inthe 1970s.See also Berkeley Software DistributionUnix; Computer Systems Research Group.benchmark A specific standard againstwhich some aspect of computer perfor-mance can be compared.A benchmark is a test that attempts toquantify hardware, software, or systemperformance—usually in terms of speed, re-liability, or accuracy. One of the majorproblems in determining performance is de-ciding which of the many benchmarksavailable actually reflects the way you in-tend to use the system.See also benchmark program.benchmark program A program thatattempts to provide a consistent measure-mentofsystemperformance.Herearesomeexamples:IDhrystone, which measures microproces-sor and memory performanceIWhetstone, which measures speed ofarithmetic operationsIKhornerstone, which measures overallsystem performance, including disk-driveaccess speed, memory access speed, andprocessor performanceThe Systems Performance Evaluation Co-operative (SPEC) developed a set of tentests to measure performance in actual ap-plication environments. The results of thesetests are known as SPECmarks.BER See bit error rate; error rate.Berkeley Software Distribution UnixAbbreviated BSD Unix, and also known asBerkeley Unix. BSD Unix was developed atthe University of California at Berkeley by2461book Page 43 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 49. Berkeley Unix44researchers working in the Computer Sys-tems Research Group (CSRG) from the1970s to 1993 when the group finallyclosed its doors. BSD added many signifi-cant advanced features to Unix, includingthe C shell, the vi editor, TCP/IP network-ing additions, and virtual memory.Because the CSRG was an academic groupproducing state-of-the-art software with nosupport obligations, BSD Unix was not sup-ported in the normal way; bug fixes weresometimes made available, but it was a hit-and-miss process at best. For this reason,BSD Unix appealed to the research commu-nity and scientific users rather than to com-mercial users who tended to use Unix fromAT&T.BSD Unix 4.1 through to the last release,version 4.4, and the related commercialproducts, including those from Sun Micro-systems, DEC, and Mt Xinu, are stillpopular and in use in universities and com-mercial institutions all over the world.See also FreeBSD; Linux; NetBSD; Unix.Berkeley Unix See Berkeley SoftwareDistribution Unix.beta site A location where beta testing isperformed before a hardware or softwareproduct is formally released for commercialdistribution.See also beta software; beta testing.beta software Software that has beenreleased to a cross-section of typical usersfor testing before the commercial release ofthe package.See also beta testing.beta testing The process of field testingnew hardware or software products beforethe product’s commercial or formal release.Beta testing is usually done by a cross-sec-tion of users, not just programmers. Thepurpose of beta testing is to expose the newproduct to as many real-life operating con-ditions as possible.If the beta tests indicate a higher-than-expected number of bugs, the developerusually fixes the problems and sends theproduct out again for another round of betatesting. Preliminary versions of the productdocumentation are also circulated for re-view during the beta testing.See also alpha testing.BGP See Border Gateway Protocol.Big Blue A nickname for InternationalBusiness Machine Corporation (IBM),which uses blue as its corporate color.big endian A computer architecture inwhich the most significant byte has the low-est address and so is stored big end first.Many processors, including those fromMotorola and Sun, certain RISC proces-sors, the PDP-11, and the IBM 3270 seriesare all big endian. The term comes fromJonathan Swift’s Gulliver’s Travels, inwhich wars were fought over whetherboiled eggs should be opened at the big endor the little end.See also holy wars; little endian.binaries A slang term for a group of bi-nary files.2461book Page 44 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 50. 45bindery emulationbinary Any scheme that uses two differ-ent states, components, conditions, orconclusions.In mathematics, the binary or base-2 num-bering system uses combinations of thedigits 0 and 1 to represent all values. Themore familiar decimal system has a base of10 (0–9).Unlike computers, people find binary num-bers that consist of long strings of zeros andones difficult to read, so most programmersuse hexadecimal (base-16) or octal (base-8)numbers instead.Binary also refers to an executable file con-taining a program.binary coded decimal AbbreviatedBCD. A simple system for converting deci-mal numbers into binary form, in whicheach decimal digit is converted into binaryand then stored as a single character.binary file A file consisting of binary in-formation. Usually, a binary file is a pro-gram or data file in machine-readable formrather than in human-readable ASCII text.You can convert a binary file into a text-based form so that you can transmit it overthe Internet.See also base64; Multipurpose InternetMail Extension.binary license A license granted to auser by a software developer, entitling theuser to run a specific software package un-der well-defined circumstances, using thebinary files provided by the developer.A binary license does not entitle the user toa copy of the source code for the package,although a certain level of configurationcan be done, and the user does not have theright to modify the software in any way be-yond this simple configuration.See also open source software; sourcelicense.BIND 1. A Novell NetWare server utilityused to bind a protocol to a network inter-face card or device driver.2. Abbreviation for Berkeley InternetName Domain, a BSD client/server pro-gram that manages host and IP addresses bymatching the host name with the IP dotteddecimal address.See also Domain Name Service; dotteddecimal.bindery A database maintained by olderNovell NetWare network operating sys-tems. The bindery contains informationabout users, servers, and other importantnetwork configuration details in a flat da-tabase. The bindery is crucial to NetWare’soperation and is constantly consulted bythe operating system.In NetWare 4.x and later systems, the bind-ery is replaced by NetWare Directory Ser-vices (NDS).See also NetWare Directory Services.bindery emulation A NetWare 4.x andlater feature that allows bindery-based util-ities to work with NetWare Directory Ser-vices (NDS) on the same network. Binderyemulation applies only to leaf objects with-in the Organizational container object.See also container object; leaf object; Net-Ware Directory Services.2461book Page 45 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 51. Bindery object46Bindery object A leaf object that repre-sents an object placed in the Directory treeby an upgrade utility, but that cannot befurther identified by NetWare DirectoryServices (NDS). The Bindery object is avail-able for the purposes of backward compat-ibility with older, bindery-based utilitiesand applications.See also leaf object; NetWare DirectoryServices.bindery services See binderyemulation.binding The process of establishing com-munications between the protocol devicedriver and the network interface card driver.BIOS Acronym for basic input/outputsystem, pronounced “bye-os.” In the PC,the BIOS is a set of instructions that tests thehardware when the computer is first turnedon, starts to load the operating system, andlets the computer’s hardware and operatingsystem communicate with applications andperipheral devices, such as hard disks,printers, and video adapters. These instruc-tions are stored in ROM as a permanentpart of the computer.As new hardware is developed, new BIOSroutines must be created to service those de-vices. For example, BIOS support has beenadded for power management and for ever-larger hard disks. If you are experiencingproblems accessing such devices after add-ing them to an existing system, your com-puters BIOS may be out of date. Contactyour computer supplier for informationabout BIOS updates.bis A term describing a secondary CCITT(Consultative Committee for InternationalTelephony and Telegraphy) recommenda-tion that is an alternative or extension to theprimary recommendation. For example,the CCITT V.42 standard refers to errorcorrection, and the V.42 bis standard refersto data compression.See also ter.B-ISDN See Broadband Integrated Ser-vices Digital Network.bisynchronous communications Aprotocol used extensively in mainframecomputer networks. With bisynchronouscommunications, both the sending and re-ceiving devices must be synchronized be-fore data transmission begins.Data is collected into a package known as aframe. Each frame contains leading andtrailing characters that allow the computerstosynchronizetheirclocks.Thestructureofa bisynchronous communications frame isshown in the accompanying illustration.The STX and ETX control characters markthe beginning and end of the message. BCCis a set of characters used to verify the ac-curacy of the transmission.A more modern form of this kind of proto-col is SDLC (Synchronous Data Link Con-trol), which is used in IBM’s proprietarynetworking scheme, SNA.See also asynchronous transmission; Syn-chronous Data Link Control.2461book Page 46 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 52. 47bit stuffingBISYNCHRONOUS COMMUNICATIONSbit Contraction of binary digit. A bit isthe basic unit of information in the binarynumbering system, representing either 0(off) or 1 (on). Bits can be grouped to formlarger storage units; the most commongrouping is the 7- or 8-bit byte.See also octet.bit error rate Abbreviated BRI. Thenumber of erroneous bits in a data trans-mission or in a data transfer, such as fromCD-ROM to memory.bit-oriented protocol A communica-tions protocol in which data is transmittedas a stream of bits rather than as a stream ofbytes.A bit-oriented protocol uses specific se-quences of bits as control codes, unlike abyte-oriented protocol, which uses reservedcharacters. HDLC (High-level Data LinkControl) and IBMs SDLC (SynchronousData Link Control) are both bit-orientedprotocols.See also byte-oriented protocol.bit rate The rate at which bits are trans-mitted over a communications channel, de-scribed in terms of bits per second (bps).See also baud rate.bits per inch Abbreviated bpi. The num-ber of bits that a tape or tape cartridge canstore per inch of length.bits per second Abbreviated bps. Thenumberofbinarydigits,orbits,transmittedevery second during a data-transfer proce-dure. Bits per second is a measurement ofthe speed of operation of equipment, suchas a computer’s data bus or a modem thatconnects a computer to a communicationscircuit.bit stuffing A technique used to ensurethat a specific bit pattern never occurs in2461book Page 47 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 53. blackout48the data transmitted over a communica-tions channel. Additional bits are added atthe transmitting end and removed at thereceiving end of the channel as the data isprocessed.blackout A total loss of commercial elec-tric power. To avoid loss of computer datadue to a blackout, use a battery-backed UPS(uninterruptible power supply).See also brownout; power conditioning.blind carbon copy Abbreviated bcc. Alist of recipients of an e-mail message whosenames do not appear in the normal messageheader, so the original recipient of the mes-sage does not know that copies have beenforwarded to other locations. Sometimescalled blind courtesy copy.block In communications, a unit of trans-mitted information that includes headercodes (such as addresses), data, and error-checking codes.See also checksum; error; error detectionand correction.blocks Sections of a tape or disk that areread or written at the same time; units ofstorage that are transferred as single units.block size The largest contiguousamount of disk space allocated by the filesystem. Files larger than the file system’sblock size may be broken into smaller frag-ments when they are stored, with sectionsof the file being stored in different loca-tions across the disk. This is known asfragmentation and, in some cases whentaken to an extreme, can severely limit sys-tem performance.The file system’s block size is often differentfrom the hard disk’s physical block size.See also fragmentation.block suballocation A mechanism usedin Novell NetWare that allows files to sharethe same block space by dividing each 8Khard-disk block into smaller 512-byte seg-ments. Files needing extra space can usethese smaller segments rather than wastinga whole new disk block, making for moreefficient disk-space screen of death AbbreviatedBSOD. An affectionate name for the screendisplayed when Microsoft Windows en-counters an error so serious that the oper-ating system cannot continue to run.Windows may also display informationabout the failure and may perform a mem-ory dump and an automatic system restart.BNC connector A small connector witha half-turn locking shell for coaxial cable,used with thin Ethernet and RG-62 cabling.The accompanying illustration shows bothmale and female connectors.BNCE See Bay Networks CertifiedExpert.BNCS See Bay Networks CertifiedSpecialist.2461book Page 48 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 54. 49bootBNC CONNECTORbookmark 1. In the Microsoft Win-dows NT Performance Monitor, a featurethat allows you to mark a point of interestin a log file and then return to that samepoint in the file at a later time.2. An option available in a Web browserthat lets you mark a Web page so that youcan identify and return to a favorite sitequickly and easily without having to retypethe URL or even remember how you gotthere.Boolean Any variable that can have alogical value of true or false. Named afterGeorge Boole, the developer of a branch ofalgebra based on the values of true andfalse, Boolean works with logical ratherthan numeric relationships.Boolean operators include AND (logicalconjunction), OR (logical inclusion), XOR(exclusive or), and NOT (logical negation)and are sometimes described as logicaloperators.Many popular Internet search engines al-low Boolean searches.See also search engine.boot To load an operating system intomemory, usually from a hard disk, althoughoccasionally from a floppy disk. Booting isgenerally an automatic procedure that be-gins when you turn on or reset your comput-er. A set of instructions contained in ROMbegins executing. The instructions run a se-ries of power-on self tests (POSTs) to checkthat devices such as hard disks are in work-ing order, locate and load the operating sys-tem, and finally pass control over to thatoperating system.Boot may be derived from the expression“pulling yourself up by your own boot-straps” and is sometimes called bootstrap.See also BIOS; cold boot; warm boot.2461book Page 49 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 55. bootable disk50bootable disk Any disk capable of load-ing and starting the operating system. Boot-able floppy disks are becoming less commonbecause operating systems are growing larg-er. In some cases, all the files needed to startthe operating system will not fit on even thelargest-capacity floppy disk, which makes itimpossible to boot from a floppy disk.BOOTCONF.SYS A Novell NetWareconfiguration file that specifies how a disk-less workstation boots the operating systemfrom the file server. If the file server con-tains several remote boot image files,BOOTCONF.SYS determines which onewill be loaded onto the workstation.See also diskless workstation.BOOTP See Bootstrap Protocol.boot ROM A type of ROM that allows aworkstation to communicate with the net-work file server and to read an image filecontaininganoperatingsystemprogram.Inthis way, a workstation without a local diskcan boot the operating system from the fileserver.See also diskless workstation.boot sector virus A virus that infectsthe master boot record of a computer byoverwriting the original boot code with in-fected boot code. This kind of virus is usu-ally spread to a hard disk from an infectedfloppy disk being used as a boot disk.See also antivirus program; file-infectingvirus; macro virus; multipart virus; poly-morphic virus; stealth virus; Trojan Horse;vaccine; virus.bootstrap See boot.Bootstrap Protocol AbbreviatedBOOTP.AnInternetprotocolthatprovidesnetwork configuration information to adiskless workstation.When the workstation first boots, it sendsout a BOOTP message on the network. Thismessage is received by the server, which ob-tains the appropriate configuration informa-tion and returns that information to theworkstation. This information includes theworkstation’s IP address, the IP address ofthe server, the host name of the server, andthe IP address of a default router.See also Dynamic Host ConfigurationProtocol.border A security perimeter formed bylogical boundaries that can only be crossedat specifically defined locations known asborder gateways.See also border gateway.border gateway Arouterthatconnectsaprivate LAN to the Internet. A border gate-way is a security checkpoint used to force allnetwork traffic, either inbound or out-bound, through a single point of control.See also border; firewall; Novell Border-Manager; router.Border Gateway Protocol Abbreviat-ed BGP. A routing protocol designed to re-place EGP (External Gateway Protocol)and interconnect organizational networks.BGP, unlike EGP, evaluates each of the pos-sible routes for the best one.Border router See Area Border router.2461book Page 50 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 56. 51bridgeBorland International, Inc. See See robot.bounce The return of an e-mail messageto its original sender due to an error in de-livery. You may have made a simple spellingmistake in the e-mail address, the recipient’scomputer system may be down, or the recip-ient may no longer subscribe to or have anaccount on the system. A returned e-mailmessage will usually contain a description ofwhy the message bounced.Bourne shell In Unix, a popular com-mand interpreter with a built-in program-ming language.The Bourne shell, developed by Dr. StevenBourne of Bell Labs, is the oldest Unix shellstill in popular use and features a built-incommand set for writing shell scripts,background execution of commands, in-put and output redirection, job control,and a set of shell variables to allow envi-ronment customization.See also Bash; C shell; Korn shell; Linux;Unix shell.bpi See bits per inch.bps See bits per second.brain damaged An expression used todescribe any poorly designed program orpiece of hardware that does not includethose features most users would consideressential. The implication is that the design-er should have known better than to leavethose features out of the product.breach A loss of network security as a re-sult of a successful attack.See also brute-force attack; dictionary at-tack; social engineering.breakout box A small device that can beconnected into a multicore cable for testingthe signals in a transmission. Small LEDs inthe breakout box indicate when a signal istransmitted over one of the lines. Switchesor short jumper cables can be used to re-route these signals to other pins as requiredfor troubleshooting.See also sniffer.BRI See Basic Rate ISDN.bridge A hardware device used to con-nect LANs so that they can exchange data.Bridges can work with networks that usedifferent wiring or network protocols, join-ing two or more LAN segments to formwhat appears to be a single network.A bridge operates at the data-link layer ofthe OSI Reference Model for computer-to-computer communications. It manages theflow of traffic between the two LANs byreading the address of every packet of datathat it receives.See also brouter; gateway; OSI ReferenceModel; router.2461book Page 51 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 57. BrightWorks52BRIDGEBrightWorks A package of networkmanagement utilities from McAfee Associ-ates that includes hardware and softwareinventory, application metering, remotecontrol of clients, virus detection, and ahelp-desk utility.Broadband Integrated Services DigitalNetwork Abbreviated B-ISDN. A high-speed communications standard for WANsthat handles high-bandwidth applications,such as video, voice, data, and graphics.SMDS (Switched Multimegabit Data Ser-vices) and ATM (Asynchronous TransferMode) are two BISDN services that canprovide a huge bandwidth.See also Asynchronous Transfer Mode;SONET; Switched Multimegabit DataServices.BROADBAND INTEGRATED SERVICES DIGITAL NETWORKbroadband network A technique fortransmitting a large amount of information,including voice, data, and video, over longdistances using the same communicationschannel. Sometimes called wideband trans-mission, it is based on the same technologyused by cable television.2461book Page 52 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 58. 53brouterThe transmission capacity is divided intoseveral distinct channels that can be usedconcurrently by different networks, nor-mally by frequency-division multiplexing(FDM). The individual channels are pro-tected from each other by guard channels ofunused frequencies. A broadband networkcan operate at speeds of up to 20Mbps.See also baseband network; multiplexer.BROADBAND NETWORKbroadcast To send a message to all userscurrently logged in to the network.See also multicast.broadcast storm Congestion on a net-work that occurs when a large number offrames are transmitted by many worksta-tions in response to a transmission from A Novell Distributed Print Servic-es (NDPS) service providing managementservices for network printers, includingevent notification and storage of printer re-sources such as device drivers.brouter A networking device that com-bines the attributes of a bridge and a router.A brouter can route one or more specificprotocols, such as TCP/IP, and bridge all2461book Page 53 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 59. brownout54others, for example, and can operate at ei-ther the data-link layer or the network layerof the OSI Reference Model.See also gateway.brownout A short period of low volt-age, often the result of an unusually heavydemand for power, that may cause yourcomputer to crash. If your area experienc-es frequent brownouts, consider using aUPS (uninterruptible power supply) as abattery backup system.browse list A list of computers and ser-vices available on a network.browser 1. Anapplicationprogramusedto explore Internet resources. A browser letsyou wander from Web site to Web site with-out concern for the technical details of thelinks between them or the specific methodsused to access them and presents the infor-mation—text,graphics,sound,orvideo—asa document on the screen.2. A small application used to scan a data-base or a list of files.3. In Windows NT networking, a mecha-nism used as a name service.See also Web browser; World Wide Web.brute-force attack A technique em-ployed by intruders that checks every pass-word in a password file against everypossible password generated sequentially.A brute-force attack is very clumsy, is usu-ally considered the last resort in an attack,takes a long time to run, and is easily de-tected by even the most modest security pre-cautions. Also called a keyspace attack.Seealso denialofserviceattack;dictionaryattack; social engineering; Trojan Horse.BSD Unix See Berkeley Software Distri-bution Unix.BSOD See blue screen of death.buffer An area of memory set aside fortemporary storage of data. Often, the dataremains in the buffer until some externalevent finishes. A buffer can compensate forthe differences in transmission or process-ing speed between two devices or between acomputer and a peripheral device, such as aprinter.Buffersareimplementedinavarietyofways,including first-in-first-out (FIFO) used forpipes and last-in-last-out used for stacks andcircular buffers such as event logs.See also pipe.buffered repeater Any device that am-plifies and retransmits a signal so that it cantravel greater distances. A buffered repeatercan also control the flow of information toprevent collisions.See also repeater.bug A logical or programming error inhardware or software that causes a mal-function of some sort. If the problem is insoftware, it can be fixed by changes to theprogram. If the fault is in hardware, newcircuits must be designed and constructed.Some bugs are fatal and may cause a pro-gram to stop responding or cause data loss,others are just annoying, and many are noteven noticeable. The term apparently orig-inates from the days of the first electrome-chanical computers, when a problem was2461book Page 54 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 60. 55bus masteringtraced to a moth caught between two con-tacts inside the machinery.See also bug fix.bug fix A release of hardware or soft-ware that corrects known bugs but does notcontain new features. Such releases are usu-ally designated by an increase in the decimalportion of the revision number; for exam-ple, the revision level may advance from 2.0to 2.01 or 2.1, rather than from 2.0 to 3.0.built-in groups The default groups pro-vided with some operating systems that de-fine a collection of rights and permissionsfor members. Using built-in groups is aneasy way of providing access to commonlyused network resources.bulletin board system AbbreviatedBBS. A computer system equipped with oneor more modems, serving as a message-passing system or centralized informationsource, usually for a particular special in-terest group. Bulletin board systems wereoften established by software vendors andby PC user groups in the past, but have beenreplaced in recent times by Web sites.bundled software Programs combinedinto a single package sold for a single price.Sales aimed at a specific target, such as themedical profession, usually bundle hard-ware with application-specific softwaresuited to that profession.See also unbundled software.burned-in address The hardware ad-dress on a network interface card (NIC).This address is assigned by the manufacturerof the interface card, which ensures that ev-ery card has a unique address.See also hardware address.burst mode A method of data transmis-sion in which information is collected andthen sent in one single high-speed transmis-sion, rather than one packet or character ata time.Systems that use multiplexers to serve sever-al channels often use burst mode to serviceeach channel in turn. Much LAN traffic canbeconsideredburstmodetransmission:longperiods of inactivity punctuated by shortbursts of intense activity. In Novell Net-Ware, burst mode is known as packet burst.bus An electronic pathway along whichsignals are sent from one part of a computerto another. A PC contains several buses,each used for a different purpose:IThe address bus allocates memoryaddresses.IThe data bus carries data between the pro-cessor and memory.IThe control bus carries signals from thecontrol unit.See also architecture; Extended IndustryStandard Architecture; Industry StandardArchitecture; local bus; MicrochannelArchitecture; Peripheral ComponentInterconnect local bus.bus mastering A technique that allowscertain advanced bus architectures to dele-gate control of data transfers between theCPU and associated peripheral devices to anadd-in board. This technique gives network2461book Page 55 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 61. bus network56interface cards (NICs) greater system busaccess and higher data-transfer speeds.In the PC, bus mastering is supported by allthe common architectures except for theolder Industry Standard Architecture.See also Extended Industry Standard Ar-chitecture;IndustryStandardArchitecture;local bus; MicroChannel Architecture;Peripheral Component Interconnect localbus.bus network In networking, a topologythat allows all network nodes to receive thesame message through the network cable atthe same time.See also ring network; star network; token-ring network.BUS NETWORKbyte Contraction of binary digit eight. Agroup of bits. In computer storage terms, abyte usually holds a single character, suchas a number, letter, or symbol. A byte usu-ally contains 8 bits, but on some older sys-tems, a byte may only have 7 bits or mayhave as many as 11.Because bytes represent a very smallamount of storage, they are usuallygrouped into kilobytes (1,024 bytes),megabytes (1,048,576 bytes), and gi-gabytes (1,073,741,824 bytes) for conve-nience when describing hard-disk capacityor computer memory size.See also octet.bytecode An intermediate form of com-puter code produced by Java and other pro-gramming languages.Most language compilers create code thatis ready to run on a specific kind of pro-cessor. Java creates the bytecode in an ab-stract, processor-independent form, whichrequires further processing before it canactually execute on a computer. When abyte-code file is downloaded into yourcomputer from a Web page, it provides 70to 80 percent of the data needed to run theJava applet; the other 20 to 30 percent isprovided by the Java run-time environ-ment, which tells the applet how to per-form on the target computer system.2461book Page 56 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 62. 57byte-oriented protocolSee also Java; Java applet; just-in-timecompiler; sandbox.byte-oriented protocol A communica-tions protocol in which data is transmittedas a series of bytes, or characters. In orderto distinguish the data from the control in-formation, the protocol uses control char-acters that have a special meaning for thetransmittingandreceivingstations.Mostofthe common asynchronous communica-tions protocols used in conjunction withmodems are byte-oriented protocols.See also bit-oriented protocol.2461book Page 57 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 63. C258CC2 One of a series of seven levels of com-puter security defined by the National Se-curity Agency.C2-level security requires that users arelogged in and tracked during their session,that all resources have owners, that objectssuch as files be protected from processesthat might damage them, that events can beaudited, and that the system has adequateprotection against intrusion.C2 security applies to a stand-alone system,so in theory a networked computer cannotbe C2-compliant; following the guidelinescan certainly help you to set up a more se-cure system.CA See certificate authority.cable modem A modem that sends andreceives signals through a coaxial cableconnected to a cable-television system,rather than through conventional tele-phone lines.Cable modems, with speeds of up to500Kbps, are faster than current conven-tional modems, but are subject to perfor-mance changes as system load increases.Theoretical data rates are much higher thanthose achieved with conventional modems;downstream rates of up to 36Mbps are pos-sible, with 3Mbps to 10Mbps likely, andupstream rates up to 10Mbps.Cabletron Systems A leading producerof Internet and intranet hardware andmanagement solutions, Cabletron is alsomoving into Gigabit Ethernet and data,voice, and video systems.For more information about Cabletron, standards National cablingstandards, concerned with the performanceof cables and connectors under conditionsof actual use, are specified by the NationalElectric Code, American National Stan-dards Institute, and Underwriters Labora-tories. Other standards have been specifiedby the Electronics Industry Association/Telecommunications Industries Associa-tion (EIA/TIA). Standards include:IANSI/EIA/TIA-568-1991 CommercialBuilding Telecommunications Wiring.IEIA/TIA TSB-36 Additional Cable Speci-fications for UTP Cables. 1991.IEIA/TIA TSB-40 TelecommunicationsSystems Bulletin—Additional Transmis-sion Specifications for UTP ConnectingHardware. 1992.IANSI/EIA/TIA-568A 1995 revises theoriginal 568 document and adds materialfrom TSB-36 and TSB-40.IANSI/EIA/TIA-569-1990 CommercialBuilding Standard for Telecommunica-tions Pathways and Spaces.IANSI/EIA/TIA-570-1991ResidentialandLight Commercial TelecommunicationsWiring Standard.2461book Page 58 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 64. 59cache bufferIANSI/EIA/TIA-606-1993AdministrationStandard for the Telecommunications In-frastructure of Commercial Buildings.IANSI/EIA/TIA-607-1994 CommercialBuilding Grounding and Bonding Re-quirements for Telecommunications.Local codes and standards may impose ad-ditional requirements.Underwriters Laboratories (UL) tests cableand other devices to determine the condi-tions under which the device will functionsafely. Two important tests for cable per-formance are:IUL-910, which tests smoke emission andflame spread for plenum cableIUL-1666, which tests smoke emission andflame spread for riser cableCAC See Connection AdmissionControl.cache Pronounced “cash.” A special areaof memory, managed by a cache controller,that improves performance by storing thecontents of frequently accessed memory lo-cations and their addresses.A memory cache and a disk cache are notthe same. A memory cache is implementedin hardware and speeds up access to mem-ory. A disk cache is software that improveshard-disk performance.When the processor references a memoryaddress, the cache checks to see if it holdsthat address. If it does, the information ispassed directly to the processor, so RAMaccess is not necessary. A cache can speedup operations in a computer whose RAMaccess is slow compared with its processorspeed, because cache memory is alwaysfaster than normal RAM.There are several types of caches:IDirect-mapped cache A location in thecache corresponds to several specific loca-tions in memory, so when the processorcalls for certain data, the cache can locateit quickly. However, since several blocksin RAM correspond to that same locationin the cache, the cache may spend its timerefreshing itself and calling main memory.IFully associative cache Informationfrom RAM may be placed in any freeblocks in the cache so that the most re-cently accessed data is usually present;however, the search to find that informa-tion may be slow because the cache has toindex the data in order to find it.ISet-associative cache Information fromRAM is kept in sets, and these sets mayhave multiple locations, each holding ablock of data; each block may be in any ofthe sets, but it will only be in one locationwithin that set. Search time is shortened,and frequently used data are less likely tobe overwritten. A set-associative cachemay use two, four, or eight sets.See also disk cache; wait state; write-backcache; write-through cache.cache buffer A Novell NetWare imple-mentation of a disk cache used to speedserver disk accesses, thereby allowingworkstations to access data more quickly.Reading data from cache memory is muchfaster than reading data from the hard disk.NetWare uses cache buffers for a variety ofpurposes:IFor use by NetWare Loadable Modules(NLMs), such as LAN drivers, databaseservers, communications servers, andprint servers2461book Page 59 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 65. cache buffer pool60ITo cache each volume’s FATITo cache files currently in useITo build a hash table of directoryinformationSee also disk cache.cache buffer pool In Novell NetWare,the amount of memory available for use af-ter the SERVER.EXE file has been loadedinto memory. Memory in the pool can beused for a variety of purposes, includingcaching the file allocation tables for eachvolume and creating a hash table of direc-tory information.See also hash table.cache controller Pronounced “cashcontroller.” A special-purpose processorwhose sole task is to manage cache memo-ry. On newer processors, such as the IntelPentium II, cache management is integrateddirectly into the processor.See also cache.cache memory Pronounced “cashmemory.” A relatively small section of veryfast memory (often static RAM) reservedfor the temporary storage of the data or in-structions likely to be needed next by theprocessor.Cache memory integrated directly onto themicroprocessor is called primary cache orL1 cache, and cache memory located in anexternal circuit is known as secondarycache or L2 cache.See also cache.caddy The flat plastic container used toload a compact disc into certain CD-ROMdisk drives. Most current CD-ROM drivesdo not require a caddy.CAE See Common ApplicationEnvironment.CAI See Computer AssociatesInternational.Caldera, Inc. A software company inProvo, Utah, that repackages one of themost popular versions of Linux under thename of OpenLinux.For more information on Caldera, modem Also known as a dial-back modem. A special modem that doesnot answer an incoming call, but instead re-quires the caller to enter a code and hang upso that the modem can return the call. Aslong as the entered code matches a previ-ously authorized number, the modem dialsthe number. Callback modems are useful ininstallations for which communicationslines must be available for remote users butdata must be protected from intruders.caller ID See automatic packet A block of data that carriesaddressing information, as well as any oth-er information needed to establish an X.25switched virtual circuit.campus network A network that con-nects LANs from multiple departments in-side a single building or set of buildings.Campus networks are LANs because theydo not include WAN services, even thoughthey may extend for several miles.canonical The usual standard Unix wayof doing something. This term has a more2461book Page 60 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 66. 61carrier signalprecise meaning in mathematics, in whichrules dictate the way that formulas are writ-ten, but in Unix, it tends to mean “accord-ing to ancient or religious law.”See also holy wars.Canon, Inc. One of the world’s leadingsuppliers of imaging products, electronicequipment, computer printers, fax ma-chines, and scanners.For more information on Canon, See Cryptography API.card A printed circuit board or adapterthat you plug into a computer to add sup-port for a specific piece of hardware.See also expansion board; expansion bus.card services Part of the software sup-port needed for PCMCIA hardware devicesin a portable computer. Card services con-trol the use of system interrupts, memory,and power management.When an application wants to access a PC-MCIA card, it always goes through the cardservices software and never communicatesdirectly with the underlying hardware. Forexample, if you use a PCMCIA modem, it isthe card services, not the applications pro-gram, that establishes which communica-tions port and which interrupts and I/Oaddresses are in use.See also device driver; PC Memory CardInternational Association; socket services.carriage return A control character(ASCII 13) that signals the print head ordisplay cursor to return to the first positionof the current line.See also line feed.carrier An analog signal of fixed ampli-tude and frequency that is combined with adata-carrying signal to produce an outputsignal suitable for transmitting data.See also carrier signal.carrier detect Abbreviated CD. An elec-trical signal sent from a modem to the at-tached computer to indicate that the modemis online.See also Data Carrier Detect; RS-232-C.Carrier Sense Multiple Access/Collision Detection AbbreviatedCSMA/CD. A baseband protocol with abuilt-in collision-detection technique. Eachnode on the network listens first and trans-mits only when the line is free. If two nodestransmit at exactly the same time and a col-lision occurs, both nodes stop transmitting.Then, to avoid a subsequent collision, eachnode waits for a different random length oftime before attempting to transmit again.Ethernet and 802.3 LANs use CSMA/CDaccess methods.See also collision; demand priority; FastEthernet; token passing.carrier signal A signal of chosen fre-quency generated to carry data; often usedfor long-distance transmissions. A carriersignal does not convey any informationuntil the data is added to the signal bymodulation and then decoded on the re-ceiving end by demodulation.2461book Page 61 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 67. cascaded star62cascaded star A network topology inwhich multiple hubs or data centers are con-nectedinasuccessionoflevels,whichpermitsmany more connections than a single level.CASCADED STARcascading menus In Microsoft Win-dows 2000, a function that presents thecontents of network drives or special fold-ers such as Control Panel as menu itemsthat can be selected by name.See also personalized menus.Castanet Acollectionofsoftware-updatetools from Marimba, Inc. that operate overthe Internet. Based on Java technology, Cas-tanet can automatically deliver software up-dates not only for Java programs, but alsofor those written in C, C++, and VisualBasic, and because only the updated contentis downloaded, performance is optimized.For more information on Castanet, also server push.Category 1–5 The Electronics IndustryAssociation/Telecommunications IndustryAssociation (EIA/TIA) 586 cabling stan-dards, sometimes abbreviated CAT 1-5, asfollows:ICategory 1 For unshielded twisted-pair(UTP) telephone cable. This cable may beused for voice, but is not suitable for datatransmissions.2461book Page 62 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 68. 63CCITT V SeriesICategory 2 For UTP cable use at speedsup to 4Mbps. Category 2 cable is similarto IBM Cabling System Type 3 cable.ICategory 3 For UTP cable use at speedsup to 10Mbps. Category 3 cable is theminimum requirement for 10BaseT and isrequired for Token Ring. This cable hasfour pairs of conductors and three twistsper foot.ICategory 4 For the lowest acceptablegrade of UTP cable for use with 16MbpsToken Ring.ICategory 5 For 100-ohm, four-wiretwisted-pair copper cable for use at speedsup to 100Mbps with Ethernet or ATM(Asynchronous Transfer Mode). This ca-ble is low-capacitance and shows lowcrosstalk when installed according tospecifications.See also cabling standards; Type 1–9cable.CAU See Controlled Access Unit.CAV See constant angular velocity.CBCP See Certified Business ContinuityProfessional.CBE See Certified Banyan Engineer.CBR See Constant Bit Rate.CBS See Certified Banyan Specialist.CCDA See Cisco Certified DesignAssociate.CCDP See Cisco Certified DesignProfessional.CCIE See Cisco Certified Internetwork-ing Expert.CCITT See Consultative Committee forInternational Telephony and Telegraphy.CCITT Groups 1–4 A set of four stan-dards for facsimile transmissions. Groups 1and 2, which are no longer used, define an-alog facsimile transmissions. Groups 3 and4 describe digital systems, as follows:ICCITT Group 3 Specifies a 9600bpsmodem to transmit standard images of203 dpi horizontally by 98 dpi verticallyin standard mode, and 203 dpi by 198 dpiin fine mode.ICCITT Group 4 Supports images up to400 dpi for high-speed transmission overa digital data network (for example, IS-DN), rather than over a dial-up telephoneline.ICCITT is now known as the InternationalTelecommunication Union.Seealso InternationalTelecommunicationUnion.CCITT V Series A set of recommendedstandards for data communications, in-cluding transmission speeds and operation-al modes, issued by CCITT, now known asthe International TelecommunicationUnion.Each standard is assigned a number, al-though not in chronological order. Highernumbers do not always indicate a newerstandard. A second or revised version isindicated by bis, and ter indicates a thirdversion.Seealso InternationalTelecommunicationUnion.2461book Page 63 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 69. CCITT X Series64CCITT X Series A set of recommendedstandards issued by CCITT to standardizeprotocols and equipment used in public andprivate computer networks. The standardsinclude transmission speeds, interfaces toand between networks, and operation ofuser hardware. CCITT is now known as theInternational Telecommunication Union.Seealso InternationalTelecommunicationUnion.CCNA See Cisco Certified NetworkAssociate.CCNP See Cisco Certified NetworkProfessional.CCP See Certified ComputingProfessional.CCP See Compression Control Protocol.CD See carrier detect.CDA See Certified DatabaseAdministrator.CDDI See Copper Distributed DataInterface.CDE See Common DesktopEnvironment.CD-I See Compact Disc-Interactive.CDIA See Certified Document ImagingArchitect.CDMA See Code Division MultipleAccess.CDP See Cisco Discovery Protocol.CDPD See Cellular Digital Packet Data.CD-R See CD-Recordable.CD-Recordable Abbreviated CD-R. Us-ing CD-R, you can write to the disc onlyonce; after that, the disc can only be readfrom and not written to.From a functional point of view, a CD-Rand a CD-ROM are identical; you can readCD-R discs using almost any CD-ROMdrive, although the processes that create thediscs are slightly different. Low-cost CD-Rdrives are available from several manu-facturers, including Kao, Kodak, Mitsui,Phillips, Ricoh, Sony, TDK, 3M, andVerbatim.See also CD ReWritable; digital video disc;Magneto-optical storage; WORM.CD ReWritable Abbreviated CD-RW. ACD format that can be written to and erasedas many as 1000 times.From a functional point of view, a CD-RWand a CD-ROM are identical, but not allCD-ROM drives can read CD-RW discs.Low-cost CD-RW drives are available fromseveral manufacturers, including Kodak,Mitsui, Phillips, and Sony.See also CD-Recordable; digital video disc;Magneto-optical storage; WORM.CD-ROM See Compact Disc—Read-Only Memory.CD-ROM disk drive A disk device thatuses compact disc technology for informa-tion storage. Many CD-ROM disk drivesalso have headphone jacks, external speak-er jacks, and a volume control.CD-ROM disk drives designed for com-puter use are more expensive than audioCD players, because CD-ROM disk drives2461book Page 64 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 70. 65central processing unitare manufactured to much higher toler-ances. If a CD player misreads a smallamount of data, the human ear probablywill not detect the difference; if a CD-ROM disk drive misreads a few bytes of aprogram, the program will not run.The two most popular CD-ROM drive in-terface cards are SCSI and ATAPI (AT At-tachment Packet Interface). ATAPI is part ofthe Enhanced IDE specification introducedby Western Digital in 1994 and lets you plugan IDE CD-ROM directly into an IDE con-troller on the system’s motherboard. OtherCD-ROM drives may use the computer’sparallel port or a PCMCIA connection.See also Compact Disc—Read-OnlyMemory.CD-ROM Extended Architecture Ab-breviated CD-ROM/XA. An extension tothe CD-ROM format, developed by Mi-crosoft, Phillips, and Sony, that allows forthe storage of audio and visual informationon compact disc so that you can play the au-dio at the same time you view the visual data.CD-ROM/XA is compatible with the HighSierra specification, also known as ISOstandard 9660.CD-ROM/XA See CD-ROM ExtendedArchitecture.CD-RW See CD ReWritable.cell Any fixed-length data packet. Forexample, Asynchronous Transfer Mode(ATM) uses 53-byte cells, consisting of48 bytes of data and 5 bytes of headerinformation.Cell Loss Priority Abbreviated CLP. Inan Asynchronous Transfer Mode (ATM)cell, a field contained in the 5-byte cellheader that defines how to drop a cell if net-work congestion occurs. The value holdspriority values, with 0 indicating a cell withthe highest priority.See also Header Error Control; PayloadType Identifier; Virtual Channel Identifier;Virtual Path Identifier.cell relay A form of packet transmissionused in Broadcast Integrated Services Dig-ital Network (B-ISDN) networks that usesa fixed-length, 53-byte cell over a packet-switched network. Also known as Asyn-chronous Transfer Mode (ATM).cell switching A term that describeshow a cellular telephone system switchesfrom one cell to the next as the signalstrength fades. The switch takes about 300milliseconds to complete and is not notice-able by the user.Cellular Digital Packet Data Abbrevi-ated CDPD. A method used in cellular com-munications and wireless modems forsending data more efficiently by using anyidle cellular channel. Capacity becomesavailable for data transmissions when avoice call is terminated or when a call isswitched from cell to cell.CDPD uses voice channels, but can switchto a new frequency if a voice transmissionbegins in the cell currently in use.central processing unit AbbreviatedCPU. The computing and control part of thecomputer. The CPU in a mainframe comput-er may be contained on many printed circuit2461book Page 65 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 71. Centrex66boards. In a minicomputer, the CPU may becontained on several boards. The CPU in aPCisusuallycontainedinasingle,extremelypowerful microprocessor.Centrex Acronym formed from CentralExchange. Services provided to a companyby the local telephone company. All theswitching takes place at the telephone com-pany’s central office rather than at the cus-tomer site, so Centrex services are easy toexpand.Centronics parallel interface A stan-dard36-pininterfaceusedtoconnectaPCtoa peripheral device, such as a printer; origi-nally developed by the printer manufacturerCentronics, Inc. The standard defines eightparallel data lines, plus additional lines forstatus and control information.See also parallel port.CERN See Conseil Européen pour laResearche Nucléaire.CERT See Computer EmergencyResponse Team.certificate An encrypted digital signa-ture used for authentication to prove thatyou are who you claim to be, either as an in-dividual, the provider of a service, the ven-dor of a product, or a corporation, or toguarantee that an e-mail message is actuallyfrom the person you think it is from andthat it has not been altered in any way dur-ing transmission.See also authentication; certificate author-ity; Secure Sockets Layer.certificate authority Abbreviated CA.A trusted organization that validates andissues certificates; often called a “trustedauthority.”Certified Application Developer forDeveloper/2000 A certification fromOracle consisting of a set of exams coveringStructured Query Language, the creation ofprocedures using Oracle Procedure Builder,using Developer/2000, and managing theuser interface.Certified Banyan Engineer Abbreviat-ed CBE. A premium certification fromBanyan designed to evaluate technicalknowledge of the Banyan VINES networkoperating system. A candidate must com-plete two required courses and pass twoexams.Certified Banyan Specialist Abbrevi-atedCBS.AbasiccertificationfromBanyandesigned to evaluate technical knowledgeof the Banyan VINES network operatingsystem. A candidate must complete one re-quired course and pass three exams. An ad-ditional certification concentrates on theintegration of Banyan’s StreetTalk ontoMicrosoft Windows 2000 servers; to com-plete this certification, you must first be-come a Microsoft Certified Professional.Certified Business ContinuityProfessional Abbreviated CBCP. A certi-fication from Disaster Recovery Institute In-ternational (DRII) that covers intermediateinformationonbusinesscontinuityplanningand disaster recovery and associated workexperience and board certification.See also Associate Business ContinuityProfessional; Master Business Continu-ity Professional.2461book Page 66 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 72. 67Certified Lotus SpecialistCertified Computing ProfessionalAbbreviated CCP. A certification from theInstitute for Certification of ComputingProfessionals designed for experienced pro-fessionals with more than four years expe-rience in a wide variety of computing andrelated tasks.Certified Database Administrator1. Abbreviated CDA. A certification fromOracle that covers knowledge of StructuredQuery Language, administration of Oracleproducts, along with backup and recovery,and system performance tuning.2. Abbreviated CDA. A certification fromSybase that covers designing, building, andsupporting Sybase SQL Server databases.See also Certified Performance and Tun-ing Specialist.Certified Document Imaging ArchitectAbbreviated CDIA. A certification from theComputer Technology Industry Association(CompTIA) that assesses skills in documentmanagement, including scanning and stor-ing documents in digital form and using op-tical character recognition software.Certified Information System AuditorAbbreviated CISA. A certification from theInformation Systems Audit and Control As-sociation (ISACA) that covers ethics, secu-rity, system organization and management,and system development, acquisition, andmaintenance.Certified Information Systems Secu-rity Professional Abbreviated CISSP.A certification from the International In-formation System Security CertificationConsortium (ISC)2designed for system secu-rity experts with at least three years of prac-tical experience. The exam covers accesscontrol systems, operations security, cryp-tography, applications and systems plan-ning, business continuity and disasterplanning, telecommunications and networksecurity, ethics, and the law.Certified Java Developer AbbreviatedCJD. An advanced certification from SunMicrosystems designed to evaluate Javaprogramming language skills.See also Certified Java Programmer.Certified Java Programmer Abbrevi-ated CJP. A certification from SunMicrosystems designed to evaluate Javaprogramming language skills.See also Certified Java Developer.Certified Lotus Professional Abbrevi-ated CLP. A certification from Lotus de-signed to evaluate a wide range of skills andknowledge of Lotus products. Several certifi-cations are available, including CLP: Applica-tion Developer, CLP: Principal ApplicationDeveloper,CLP:SystemAdministrator,CLP:Principal System Administrator, CLP:cc:Mail System Administrator.See also Certified Lotus Specialist.Certified Lotus Specialist AbbreviatedCLS. A certification from Lotus designed toevaluate knowledge of a single Lotus prod-uct. Options include certification in LotusDomino, Lotus 1-2-3, Lotus Notes, andcc:Mail.See also Certified Lotus Professional.2461book Page 67 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 73. Certified Network Professional68Certified Network Professional Ab-breviated CNP. A certification from theNetwork Professional Association (NPA)that involves meeting requirements in theareas of client operating systems, network-ing hardware, network operating systems,communications protocols, and networktopologies. Two years of relevant work ex-perience and two vendor-based certifica-tions are required to complete the program.Certified Novell Administrator Abbre-viated CNA. A Novell certification programfor network administrators responsible forthe day-to-day operation of a network.Within the CNA program, a candidate canspecialize in one or more Novell products,including IntranetWare, NetWare, orGroupWise.See also Certified Novell Engineer; MasterCertified Novell Engineer.Certified Novell Engineer AbbreviatedCNE. A Novell certification program fortechnical professionals concerned with net-work system design, implementation, andmaintenance. Within the CNE program, acandidate can specialize in one or more No-vell products, including IntranetWare, Net-Ware, or GroupWise.See also Certified Novell Administrator;Master Certified Novell Engineer.Certified Novell Engineer ProfessionalAssociation Abbreviated CNEPA. Anassociation of Certified Novell Engineers(CNEs) that provides benefits, such asworkshops demonstrating how to config-ure and troubleshoot Novell products, aswell as admission to network-related eventsand complementary subscriptions.See also Certified Novell Engineer.Certified Novell Instructor Abbreviat-ed CNI. A Novell certification program fortrainers who want to teach Novell courses.Once certified, by passing the appropriateexam at the instructor level, a CNI canteach any instructor-led Novell course, in-cluding those for Certified Novell Admin-istrator (CNA), Certified Novell Engineer(CNE), and Master CNE (MCNE).See also Master Certified Novell Instructor.Certified Performance and TuningSpecialist Abbreviated CPTS. A certifi-cationfromSybasethattestsforproficiencyacross a wide range of database administra-tion, tuning, and performance concepts.See also Certified Database Administrator.Certified PowerBuilder DeveloperAssociate Abbreviated CPDA. A certifi-cation from Sybase designed for experi-enced PowerBuilder developers that testsknowledge in the areas of client/server ar-chitecture, object-oriented programming,relational databases, and Structured QueryLanguage.Seealso CertifiedPowerBuilderDeveloperProfessional.Certified PowerBuilder DeveloperProfessional Abbreviated CPDP. A certi-fication from Sybase designed for experi-encedPowerBuilderdevelopersthatrequireshands-on experience building PowerBuilderapplications as well as a demonstration ofgood development practices.2461book Page 68 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 74. 69characterSeealso CertifiedPowerBuilderDeveloperAssociate.Certified Solutions Expert Abbreviat-ed CSE. A pair of Internet certificationsfrom IBM. CSE: Net.Commerce is aimedat the developers of Internet store frontsand other financial transactions over theInternet. CSE: Firewall is a security-relatedcertification.Certified Unicenter Engineer Abbrevi-ated CUE. A certification from ComputerAssociates designed to evaluate expertise inthe Unicenter TNG product line.CGI See Common Gateway Interface.Challenge-Handshake AuthenticationProtocol Abbreviated CHAP. A methodof authentication that you can use whenconnecting to an ISP that allows you to logon automatically.See also Password AuthenticationProtocol.challenge-response authentication Amethod of authentication used by MicrosoftWindows 2000 and other operating systems.When a user contacts a server, the server re-sponds with a challenge, upon which theuser then performs a cryptographic opera-tion and returns the result to the server. Theserver then performs the same operation,and if the two results are the same, the useris considered authentic.See also clear text 1. In communications, any con-necting path that carries information froma sending device to a receiving device. Achannel may refer to a physical medium (forexample, a coaxial cable) or to a specificfrequency within a larger channel.2. In Internet Relay Chat (IRC), a namedforum where you can chat in real time withother users; also known as a chat room.channelization The process of dividingthe bandwidth of a communications circuitinto smaller increments.See also T1.channelized T1 See T1.Channel Service Unit AbbreviatedCSU. A device that functions as a certifiedsafe electrical circuit, acting as a bufferbetween the customer’s equipment and apublic carrier’s WAN.A CSU prevents faulty CPE (customer-pre-mises equipment), such as DSUs (data ser-vice units), from affecting a public carrier’stransmission systems and ensures that allsignals placed on the line are appropriatelytimed and formed. All CSU designs must beapproved and certified by the FCC.See also Data Service Unit.CHAP See Challenge-HandshakeAuthentication Protocol.character A symbol that corresponds to akey on the keyboard. A character can be a let-ter, a number, punctuation, or a special sym-bol and is usually stored as a single byte. Acollection of related characters is known as acharacter set, and the most common charac-ter set on PC systems is the American Stan-dard Code for Information Interchange(ASCII). Some larger IBM systems still useExtendedBinaryCodedDecimalInterchange2461book Page 69 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 75. character-based interface70Code (EBCDIC). In an attempt to rationalizethe many international character sets in usethese days, some systems use more than onebyte to store a character.See also American Standard Code forInformation Interchange; Extended Bi-nary Coded Decimal Interchange Code;Unicode.character-based interface An operat-ing system or application that uses textcharacters rather than graphical techniquesfor the user interface.See also command line; graphical userinterface.character code A code that representsone specific alphanumeric or control char-acter in a set of characters.See also American Standard Code forInformation Interchange; ExtendedBinary Coded Decimal Interchange Code;Unicode.character mode A mode in which thecomputer displays characters on the screenusing the built-in character set, but does notshow any graphics characters or a mousepointer. Also known as text mode.character set A standard group of let-ters, numbers, punctuation marks, specialsymbols, and control characters used by acomputer.See also American Standard Code forInformation Interchange; ExtendedBinary Coded Decimal Interchange Code;Unicode.characters per second Abbreviatedcps. The number of characters, or bytes,transmitted every second during a datatransfer. A measurement of the speed of op-eration of equipment, such as serial printersand terminals.character string Any group of alphanu-meric characters treated as a single unit.Also known as a string.cheapernet wire See thin Ethernet.checkpointing The process of movingtransactions from the transaction log totheir permanent disk location.checksum A method of providing infor-mation for error detection, usually calculat-ed by summing a set of values.The checksum is usually appended to theend of the data that it is calculated from sothat they can be compared. For example,Xmodem, a popular file-transfer protocol,uses a 1-byte checksum calculated by add-ing all the ASCII values for all 128 databytes and ignoring any numeric overflow.The checksum is added to the end of theXmodem data packet. This type of check-sum does not always detect all errors. In lat-er versions of the Xmodem protocol,cyclical redundancy check (CRC) is used in-stead for more rigorous error control.See also cyclical redundancy check; errordetection and correction.child domain In Microsoft Windows2000 Server, a secondary domain beneaththe top-level domain in a Windows 2000domain tree.2461book Page 70 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 76. 71Cisco Certified Internetworking ExpertSee also first-layer domain; parent do-main; root domain.chip A slang expression for integratedcircuit.See also integrated circuit.choke packet A packet used for flowcontrol. A node that notices congestion onthe network generates a choke packet andsends it toward the source of the conges-tion, which is then required to reduce itssending rate.CHRP See Common Hardware Refer-ence Platform.CICS See Customer Information Con-trol System.CIDR See Classless Inter-DomainRouting.CIFS See Common Internet File System.CIOS See Internetworking OperatingSystem.circuit 1. A communications channel orpath between two devices capable of carry-ing electrical current.2. A set of components connected to per-form a specific task.circuit switching A temporary commu-nications connection established as re-quired between the sending and receivingnodes. Circuit switching is often used inmodem communications over dial-up tele-phone lines. It is also used in some privatelymaintained communications networks.See also message switching; packetswitching; virtual circuit.Cirrus Logic, Inc. A leading manufac-turer of integrated circuits, particularlysemiconductor wafers, Cirrus Logic hasalso moved into the areas of 56K modemchip sets and sound-card chip sets.For more information on Cirrus Logic, See CompuServe.CISA See Certified Information SystemAuditor.CISC See complex instruction setcomputing.ciscoBus The bus used in routers fromCisco Systems, Inc.See also Cisco Extended Bus; switchprocessor.ciscoBus controller See switchprocessor.Cisco Certified Design Associate Ab-breviated CCDA. A certification from Ciscodesigned to evaluate knowledge of relativelysimple networks.See also Cisco Certified DesignProfessional.Cisco Certified Design ProfessionalAbbreviated CCDP. A certification fromCisco designed to evaluate knowledge ofcomplex networks based on Cisco LANand WAN routers and LAN switches.See also Cisco Certified Design Associate.Cisco Certified InternetworkingExpert Abbreviated CCIE. An advancedcertification from Cisco offered in three2461book Page 71 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 77. Cisco Certified Network Associate72areas: CCIE-Routing and Switching, CCIE-Internet Service Provider (ISP) Dial, andCCIE-WAN Switching.Cisco Certified Network AssociateAbbreviated CCNA. A certification fromCiscodesignedtoevaluatenetworksupportknowledge.See also Cisco Certified NetworkProfessional.Cisco Certified Network ProfessionalAbbreviated CCNP. An advanced certifica-tion from Cisco designed to evaluate net-work support knowledge.See also Cisco Certified NetworkAssociate.Cisco Discovery Protocol AbbreviatedCDP. A proprietary Cisco protocol thatruns on all hardware made by Cisco, in-cluding routers, switches, access servers,and bridges.CDP is both protocol- and media-independent. A router running CDP canadvertise its existence to other routers andcan discover a directly connected neigh-bor’s port and hostname information, aswell as hardware model number and sys-tem capabilities.Cisco Extended Bus Abbreviated Cx-Bus. The extended bus used in routers fromCisco Systems, Inc.See also ciscoBus; switch processorCisco Systems, Inc. The world’s lead-ing manufacturer of routers and internet-working hardware and software products.More than 80 percent of the backbone rout-ers currently in use on the Internet weremade by Cisco, and its Internetwork Oper-ating System (IOS) is quickly becoming anindustry standard that other vendors are in-corporating into their own products.For more information on Cisco, Device management soft-ware for Cisco networking devices. Cisco-View provides troubleshooting and devicemonitoring functions and can be used inconjunction with Simple Network Manage-ment Protocol (SNMP) products.See also Simple Network ManagementProtocol.Ciscoworks A set of management appli-cations from Cisco Systems, Inc., designedfor use with Cisco routers.CISSP See Certified Information Sys-tems Security Professional.CIX See Commercial Internet Exchange.CJD See Certified Java Developer.CJP See Certified Java Programmer.cladding The transparent material, usu-ally glass, that surrounds the core of an op-tical fiber. Cladding has a lower refractiveindex than the core and so prevents the lightsignal from spreading out due to modal dis-persion, by reflecting the signal back intothe central core. This helps to maintain thesignal strength over long distances.See also dispersion.Class A certification An FCC certifica-tion for computer equipment, includingmainframe computers and minicomputers2461book Page 72 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 78. 73Classless Inter-Domain Routingdestined for industrial, commercial, or of-fice use, rather than for personal use athome. The Class A commercial certifica-tion is less restrictive than the Class Bcertification for residential use, because itassumes that most residential areas aremore than 30 feet from any commercialcomputer equipment.See also Class B certification.Class A network In the IP addressingscheme, a very large network. The high-or-der bit in a Class A network is always zero,leaving 7 bits available to define 127 net-works. The remaining 24 bits of the addressallow each Class A network to hold asmany as 16,777,216 hosts. Examples ofClass A networks include General Electric,IBM, Hewlett-Packard, Apple Computer,Xerox, Digital Equipment Corporation,and MIT. All the Class A networks are inuse, and no more are available.See also address classes; IP address.Class B certification An FCC certifica-tion for computer equipment, includingPCs, laptops, and portables destined for usein the home rather than in a commercial set-ting. Class B levels of radio frequency inter-ference (RFI) must be low enough so thatthey do not interfere with radio or televi-sion reception when there is more than onewall and 30 feet separating the computerfrom the receiver. Class B certification ismore restrictive than the commercial ClassA certification.See also Class A certification.Class B network In the IP addressingscheme,amedium-sizednetwork.The2high-order bits are always 10, and the remainingbits are used to define 16,384 networks, eachwith as many as 65,535 hosts attached. Ex-amplesofClassBnetworksincludeMicrosoftand Exxon. All Class B networks are in use,and no more are available.See also address classes; IP address.Class C network In the IP addressingscheme, a smaller network. The 3 high-or-der bits are always 110, and the remainingbits are used to define 2,097,152 networks,but each network can have a maximum ofonly 254 hosts. Class C networks are stillavailable.See also address classes; IP address.Class D network In the IP addressingscheme, a special multicast address thatcannot be used for networks. The 4 high-or-der bits are always 1110, and the remaining28 bits allow access to more than 268 mil-lion possible addresses.See also address classes; IP address.Class E network In the IP addressingscheme, a special address reserved for ex-perimental purposes. The first 4 bits in theaddress are always 1111.See also address classes; IP address.classes In Novell Directory Services, anobject can be defined as an instance ofan object class. Classes include User,Group, Printer, Print Server, Computer,and so on.Classless Inter-Domain Routing Ab-breviated CIDR, pronounced “cider.” Aninterim solution to the problem that the In-ternet is running out of addresses.2461book Page 73 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 79. cleartext74Blocks of Class C addresses are assigned toa site based on the number of addresses thatsite requires, to prevent wasted addresses.Also, the Class C address space is dividedinto four major areas—Europe, NorthAmerica, Central and South America, andAsia and the Pacific—and each zone is as-signed 32 million addresses.CIDR networks are often described as“slash x” networks; the x represents thenumber of bits in the IP address range con-trolled by the granting authority. For exam-ple, a Class C network in CIDR termsbecomes a slash 24 network.See also address classes; IP address.cleartext Text that has not been encrypt-ed in any way and that can be interceptedand read easily while in transit; usually ap-plied to an unencrypted password.See also plaintext.clear text authentication An authenti-cation method that encodes user name andpassword information according to a freelyavailable 64-bit encoding utility.See also challenge-response authentica-tion; encryption.Clear to Send Abbreviated CTS. Ahardware signal defined by the RS-232-Cstandard that indicates that the transmis-sion can proceed.See also RS-232-C; Request to Send.CLEC See Competitive Local ExchangeCarrier.client A device or application that usesthe services provided by a server.A client may be a PC or a workstation on anetwork using services provided from thenetwork file server, or it may be that part ofan application program that runs on theworkstation supported by additional soft-ware running on the server.One of the most familiar clients is the Webbrowser.See also client/server architecture; DOS cli-ent; Macintosh client; OS/2 client; Unixclient; Windows client.client application In OLE, the applica-tion that starts a server application to ma-nipulate linked or embedded information.client pull A mechanism used on the In-ternet whereby a client application, usuallya Web browser, initiates a request for ser-vices from a Web site.See also server push.Client Services for NetWare A soft-ware package included with MicrosoftWindows 2000 that connects a Windows2000 client to a Novell NetWare file server.client/server architecture A comput-ing architecture that distributes processingbetween clients and servers on the network.In the past, traditional computing has reliedon a hierarchical architecture based on non-programmable dumb terminals connectedto a mainframe computer. In this scheme,the database was on the same computerthat was running the application. A client/server approach replaces this structure bydividing the application into two separateparts: a front-end client and a back-end2461book Page 74 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 80. 75clockserver, usually referred to as a client and aserver.The client component provides the userwith the power to run the data-entry part ofthe application, and this part of the client isusually optimized for user interaction withthe system.The server component, which can be eitherlocal or remote, provides the data manage-ment, administration, and system securityfeatures and manages information sharingwith the rest of the network.In other words, clients request informationfrom the servers, and the servers store dataandprogramsandprovidenetworkservicesto clients.Client/server architecture can sustain sever-al levels of organizational complexity, in-cluding the following:IStand-alone (non-networked) client ap-plications, such as local word processorsIApplications that run on the client butrequest data from the server, such asspreadsheetsIPrograms that use server capabilities toshare information among network users,such as electronic mail systemsIPrograms in which the physical search ofrecords takes place on the server, while amuch smaller program running on the cli-ent handles all user-interface functions,such as database applicationsClient/server computing lightens the pro-cessing load for the client PCs, but increasesthe load on the server. For this reason, serv-er computers tend to have larger and fasterhard-disk drives and much more memoryinstalled than conventional file servers. Theserver may also be a minicomputer or amainframe computer.Typically, a client/server approach reducesnetwork traffic, because relatively smallamounts of data are moved over the net-work. This is in sharp contrast to the typicalnetwork, in which entire files are constantlybeing transmitted between the workstationand the file server.Database applications were some of thefirst to embrace the client/server concept,particularly those using Structured QueryLanguage (SQL). SQL has grown into an in-dustry standard database language; it is rel-atively easy to implement, it is robust andpowerful, and it is easy for users to learn.See also network computer; thin client.client-side caching See offline files.Clipper chip A low-cost encryption de-vice backed by the U.S. federal government.The chip would allow businesses to trans-mit encoded messages, but at the same time,allow certain government agencies to inter-cept and decode the messages if criminal ac-tivities were suspected. Needless to say, thisproposal has generated a lot of intense dis-cussion, particularly from civil rightsgroups concerned with an individual’s rightto privacy and other ethical issues; otherpotential users want access to the best avail-able encryption systems, not just those putforward by the government.CLNP See Connectionless NetworkProtocol.clock An electronic circuit that generatesregularly spaced timing pulses at speeds up2461book Page 75 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 81. clock-multiplying76to millions of cycles per second. These puls-es are used to synchronize the flow of infor-mation through the computer’s internalcommunications channels.See also clock speed.clock-multiplying Amechanismusedbysome Intel processors that allows the chipto process data and instructions internallyat a speed different from that used by therest of the system.clock speed The internal speed of a com-puter or processor, normally expressed inmegahertz (MHz). Also known as clock rate.The faster the clock speed, the faster thecomputer will perform a specific operation(assuming the other components in thesystem, such as disk drives, can keep upwith the increased speed).The Intel 8088 processor used in the originalIBM PC had a clock speed of 4.77MHz—painfully slow when compared with speedsused by current processors, which can run atclock speeds of several hundred MHz.clone Hardware that is identical in func-tion to an original.For example, an IBM clone is a PC that usesan Intel (or similar) microprocessor andfunctions in the same way as the IBM PCstandard. A Macintosh clone functions inthe same way as a computer manufacturedby Apple Computer, Inc.Although most clones do perform as in-tended, small internal differences can causeproblems in some cases. It can be difficult toensure consistency of components and levelof operation when using a number of clonespurchased over a long period of time.See also Advanced Micro Devices, Inc.;Cyrix.closed architecture A design that doesnot allow for easy, user-supplied additions.This term is often used to describe some ofthe early Macintosh computers, which didnot allow easy expansion of the system withadd-in cards. Closed architecture can alsorefer to a computer design whose specifica-tions are not published or generally avail-able, making it impossible for third-partycompanies to provide products that workwith the computer.See also open architecture.CLP See Cell Loss Priority; CertifiedLotus Professional.CLS See Certified Lotus Specialist.CLTP See Connectionless TransportProtocol.cluster controller An IBM or IBM-com-patible device located between a group of3270 terminals and the mainframe comput-er. The cluster controller communicates be-tween the computer and the terminals usingSDLC (Synchronous Data Link Control) ora bisynchronous communications protocol.clustering A fault-tolerant technologydesigned to keep server availability at a veryhigh level.Clustering groups servers and other net-work resources into a single system; if oneof the servers in the cluster fails, the otherservers can take over the workload. Clus-tering software also adds a load-balancingfeature to make sure that processing is2461book Page 76 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 82. 77codecdistributed in such as way as to optimizesystem throughput.CLV See constant linear velocity.CMIP See Common Management Infor-mation Protocol.CMIS See Common Management Infor-mation Services.CMOS See Complementary Metal-Oxide Semiconductor.CNA See Certified Novell Administrator.CNE See Certified Novell Engineer.CNEPA See Certified Novell EngineerProfessional Association.CNI See Certified Novell Instructor.CNP See Certified NetworkProfessional.coax See coaxial cable.coaxial cable Abbreviated coax, pro-nounced “co-ax.” A high-capacity cableused in networking that contains a solid in-nercopperconductorsurroundedbyplasticinsulation, and an outer braided copper orfoil shield.Coaxial cable is used for broadband andbaseband communications networks (andfor cable television), because the cable isusually free from external interference andpermits high transmission rates over longdistances.See also fiber-optic cable; RG-58; RG-59;RG-62; thick Ethernet; thin Ethernet.COAXIAL CABLEcodec 1. Acronym for coder/decoder,pronounced “coe-deck.” A device thatconverts analog signals (such as voice orvideo) into a digital bit stream suitable fortransmission and then converts those dig-ital signals back into analog signals at thereceiving end.2461book Page 77 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 83. Code Division Multiple Access782. Acronym for compression/decompres-sion, pronounced “coe-deck.” An overallterm to describe the hardware and softwareused in processing animation, digital video,and stereo-quality audio.See also lossless compression; lossycompression.Code Division Multiple Access Abbre-viated CDMA, also known as spread spec-trum. A digital cellular standard approvedby the Telecommunications Industry Asso-ciation (TIA) in 1993 and known as IS-95.CDMA combines both data and voice intoa single wireless network and can provideusers with digital voice services, voice mail,text messaging, and caller ID. CDMA alsoincreases system capacity up to 10 timesthat of analog systems.See also Advanced Mobile Phone Service;Cellular Digital Packet Data; wirelesscommunications.cold boot The computer startup processthat begins when you turn on power to thecomputer. You are doing a cold boot whenyou first turn on your computer. A coldboot might also be necessary if a programor the operating system crashes and freezesentirely. If your keyboard is operational, awarm boot may suffice.See also boot; warm boot.collaboration software A set of net-work-basedapplicationsthatletusersshareinformation quickly and easily.See also whiteboard.collision In networking or communica-tions, an attempt by two nodes to send amessage on the same channel at exactly thesame moment.See also Carrier Sense Multiple Access/Collision Detection; token-ring network.colon The symbol used after the protocolname in a URL.See also Uniform Resource Locator.COM See Common Object Model; Com-ponent Object Model.COM 1–4 See COM port.command interpreter See commandprocessor.command line Any interface betweenthe user and the command processor thatallows you to enter commands from thekeyboard for execution by the operatingsystem.See also graphical user interface; shell;text mode.command-line argument A parameterthat alters the default mode of a command.In many operating systems, a command-line argument is one or more letters ornumbers preceded by the / (slash) charac-ter. In Unix, a command-line argumentmay be called an option or a flag and isusually a single character preceded by a hy-phen (as in -r). With some commands, youcan group several switches. Sometimescalled a command-line switch.See also command line.command processor The part of theoperating system that displays the com-mand prompt on the screen, interprets and2461book Page 78 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 84. 79Common Hardware Reference Platformexecutes all the commands and filenamesthat you enter, and displays error messageswhen appropriate. Also called the com-mand interpreter. The command processoralso contains the system environment.command prompt A symbol (characteror group of characters) on the screen thatlets you know that the operating system isavailable and ready to receive input.Commercial Internet Exchange Ab-breviated CIX, pronounced “kicks.” A con-nection point between ISPs.A location where top-tier ISPs maintain therouters used to route packets between theirrespective network segments.Common Application EnvironmentAbbreviated CAE. A set of standards, devel-oped by X/Open for application develop-ment, including standards for the operatingsystem, compilers, software developmenttools, data management, networking, andthe graphical user interface.common carrier A communicationscompany, such as AT&T or MCI, that pro-vides data and voice telecommunicationservices to the general public.See also Postal Telephone and Telegraph.Common Desktop Environment Ab-breviated CDE. A set of specifications de-veloped by the Common Open SoftwareEnvironment (COSE) that defines an APIfor a common Unix graphical user inter-face. The specifications cover the interop-erability of applications across differenthardware platforms, multimedia andnetworking operations, as well as object-oriented technology and system adminis-tration issues.Common Gateway Interface Abbrevi-ated CGI. A standard way that programscan interface with Web servers and allowthem to run applications such as search en-gines and to access databases and otherback-end applications.CGI defines the field specifics and controltags to be placed in an HTML document,the environment variables where the Webserver places information for use by scripts,and the flow of information between clientWeb browser, the server, and the Web serv-er scripts. CGI is platform-independent.See also HyperText Markup Language;script; Web server.Common Internet File System Abbre-viated CIFS. A file system supported by Mi-crosoft, DEC, Data General, SCO, andothers, which allows users and organiza-tions to run file systems over the Internet.CIFS is an extension to Microsoft’s ServerMessage Blocks (SMB) file-sharing proto-col and allows users to share files over theInternet in the same way that they sharefiles using networking services on Windowsclients.See also WebNFS.Common Hardware ReferencePlatform Abbreviated CHRP. An openhardware architecture, based on the Power-PC and originally defined by IBM, that en-sures compatibility between systems madeby different manufacturers.2461book Page 79 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 85. Common Management Information Protocol80Common Management InformationProtocol Abbreviated CMIP. The OpenSystems Interconnection (OSI) manage-ment information protocol for networkmonitoring and control information, desig-nated ISO 9596.CMIP includes fault management, configu-ration management, performance manage-ment, and security and accountingmanagement. It is not widely available.See also Common Management Informa-tion Services; Simple Network Manage-ment Protocol.Common Management InformationServices Abbreviated CMIS. The OpenSystems Interconnect (OSI) standard func-tions for network monitoring and control.See also Common Management Informa-tion Protocol.Common name In Novell DirectoryServices, every object has a name that isunique within its context in the directorystructure. This name is known as the Com-mon name when it refers to users, nodes, orservers.See also Distinguished Name.Common Object Model AbbreviatedCOM. A specification from Microsoft andDEC to provide cross-platform interopera-bility across non-Windows platforms.COM was developed to allow networks us-ing Microsoft’s OLE technology to commu-nicate with networks using DEC’s Object-Broker technology.Common Object Request BrokerArchitecture Abbreviated CORBA. Astandard from the Object ManagementGroup (OMG), whose members includeSunMicrosystems,Hewlett-Packard,DEC,and IBM, that enables communications be-tween distributed object-oriented applica-tions, regardless of the language they arewritten in and the hardware platform onwhich they run.CORBA uses Object Request Brokers to setup communications between objects and toinvoke methods on behalf of these objects.CORBA competes with Microsoft’s Dis-tributed Component Object Model(DCOM) and ActiveX technology.See also Distributed Component ObjectModel.Common Open Software Environ-ment Abbreviated COSE, pronounced“cosy.” An industry group consisting of al-most 100 members, organized to develop astandard graphical user interface for Unix,known as the Common Desktop Environ-ment, or CDE. Original members includedSun Microsystems, Hewlett-Packard, IBM,SCO, and the UNIX Systems Group.Common Programming Interface forCommunications Abbreviated CPI-C.A cross-platform API from IBM that inter-faces to the Advanced Program-to-ProgramCommunications (APPC) environment.CPI-C is designed to support a common en-vironment for application execution acrossseveral IBM operating systems, includingMVS, VS, OS/400, and OS/2-based systems.2461book Page 80 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 86. 81Compact Disc-InteractiveSee also Advanced Peer-to-Peer Network-ing; Advanced Program-to-ProgramCommunications; Advanced InteractiveExecutive; Multiple Virtual Storage.common share In Microsoft Windows2000, system elements automaticallyshared by default when the operating sys-tem is installed or upgraded. Many com-mon shares are also hidden shares.See also default shares; hidden share;share; sharing.communications/modem server In anetwork, a server equipped with a bank ofmodems, which can be shared by users foroutgoing calls.See also access server.communications parameters Any ofseveral settings required to allow comput-ers to communicate successfully. In asyn-chronous transmissions, commonly used inmodem communications, the settings forbaud rate, number of data bits, number ofstop bits, and parity parameters must all becorrect.communications protocol 1. A stan-dard way of communicating between com-puters or between computers and terminals.Communications protocols vary in com-plexity, ranging from Xmodem, a simplefile-transfer protocol used to transfer filesfrom one PC to another, to the seven-layerOSI Reference Model used as the theoreticalbasis for many large, complex computernetworks.2. A hardware interface standard, such asRS-232-C.communications satellite A satellite ingeostationary orbit, acting as a microwaverelay station. The satellite receives signalsfrom a groundstation, amplifies them, andretransmits them on a different frequencyto another groundstation.See also downlink; propagation delay;uplink.compact disc Abbreviated CD. A non-magnetic, polished, optical disc used to storelarge amounts of digital information. A CDcan store approximately 650MB of informa-tion, equivalent to more than 1700 low-density floppy disks. This storage capacitytranslatesintoapproximately300,000pagesof text or 72 minutes of music, all on a single4.72-inch disc.Digital information is stored on the com-pact disc as a series of microscopic pits andsmooth areas that have different reflectiveproperties. A beam of laser light shines onthe disc so that the reflections can be detect-ed and converted into digital data.See also CD-Recordable; CD ReWritable;CD-ROM Extended Architecture; CompactDisc-Interactive; Compact Disc—Read-Only Memory; digital video disc.Compact Disc-Interactive Abbreviat-ed CD-I. A hardware and software stan-dard disc format for data, text, audio, stillvideo images, and animated graphics. Thestandard also defines methods of encodingand decoding compressed data, as well asdisplaying data.See also compact disc; Compact Disc—Read-Only Memory.2461book Page 81 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 87. Compact Disc—Read-Only Memory82Compact Disc—Read-Only MemoryAbbreviated CD-ROM. A high-capacity,optical storage device that uses the sametechnology used to make ordinary musicdiscs to store large amounts of information.A single 4.72-inch disc can hold up to650MB.CD-ROMs are important components ofmultimedia applications. They are alsoused to store encyclopedias, dictionaries,and other large reference works, as well aslibraries of fonts and clip art for desktoppublishing. CD-ROMs have replaced flop-py disks as the distribution mechanism forsoftware packages, including network op-erating systems and large applications; youcan load the whole package from a singlecompact disc, and you can load an operat-ing system from a set of discs.A CD-ROM uses the constant linear veloc-ity data encoding scheme to store informa-tion in a single, spiral track, divided intomany equal-length segments. To read data,the CD-ROM disk drive must increase therotational speed as the read head gets closerto the center of the disk and must decreaseas the head moves back out.See also CD-Recordable; Compact Disc-In-teractive; constant angular velocity; HighSierra specification.Compaq Computer Corporation Oneof the world’s largest computer manufac-turers, Compaq recently acquired the Digi-tal Equipment Corporation (DEC), whichboosted the company into the top threealong with IBM and Hewlett-Packard.By acquiring DEC, Compaq gained aworld-wide service and support structure,as well as access to DEC’s highly regardedhardware and software products.Compaq also shook up the computer indus-try when it introduced the first PC that costless than $1,000.For more information about Compaq, The extent to which a giv-en piece of hardware or software conformsto an accepted standard, regardless of theoriginal manufacturer.In hardware, compatibility is often ex-pressed in terms of widely accepted mod-els—this designation implies that the devicewill perform in the same way as the stan-dard device.In software, compatibility is usually de-scribed as the ability to read data file formatscreated by another vendor’s software or theability to work together and share data.See also plug-compatible.Competitive Local Exchange CarrierAbbreviated CLEC. A term coined from theTelecommunications Act of 1996 to de-scribe the deregulated, competitive phonecompanies that will be able to offer local ex-change service as well as long distance andinternational services, Internet access, andcable and video on-demand services.See also Incumbent Local Exchange Carri-er; Local Exchange Carrier.compiler A program that converts a setof program language source code state-ments into a machine-readable form suit-able for execution by a computer.2461book Page 82 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 88. 83compressed fileMost compilers do much more than this,however; they translate the entire programinto machine language, while at the sametime, they check your source code syntaxfor errors and then post error messages orwarnings as appropriate.See also just-in-time compiler.Complementary Metal-OxideSemiconductor Abbreviated CMOS,pronounced “See-moss.” A type of inte-grated circuit used in processors and formemory. Because CMOS devices operate atvery high speeds and use little power, theygenerate little heat. In the PC, battery-backed CMOS memory is used to store op-erating parameters, such as the hard disktype, when the computer is switched off.complex instruction set computingAbbreviated CISC, pronounced “sisk.” Aprocessor that can recognize and executemore than 100 different assembly-language,or low-level, instructions. CISC processorscan be powerful, but the instructions take ahigh number of clock cycles to execute.This complexity is in contrast to the sim-plicity of reduced instruction set computing(RISC) processors, in which the number ofavailable instructions has been cut to a min-imum. RISC processors are common inworkstations and can be designed to run upto 70 percent faster than CISC processors.See also assembly language; reducedinstruction set computing.Component Object Model Abbreviat-ed COM. A specification from Microsoftthat defines how objects interact in theWindows environment.COM components can be written in anyprogramming language and can be addedto or removed from a program withoutrequiring recompilation. COM is the foun-dation of the Object Linking and Embed-ding (OLE) and ActiveX specifications.See also ActiveX; Common Object Re-quest Broker Architecture; DistributedComponent Object Model.COM port In MS-DOS and MicrosoftWindows, the device name used to denote aserial communications port. In versions ofMS-DOS after 3.3, four COM ports aresupported: COM1, COM2, COM3, andCOM4. Earlier versions support onlyCOM1 and COM2.compound document A document filethat consists of information created by twoor more applications, for example, a data-base document embedded within a word-processing document.Object Linking and Embedding (OLE) canlink and embed documents and can beused to start the appropriate applicationprogram.See also Object Linking and Embedding.compressed file A file that has beenprocessed by a special utility so that it oc-cupies as little hard-disk space as possible.When the file is needed, the same programdecompresses the file back into its originalform so that it can be read by the computer.Popular compression techniques includeschemes that replace commonly occurringsequences of characters by tokens that takeup less space. Some utilities use Huffman2461book Page 83 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 89. Compression Control Protocol84coding to shrink a file, and others use adap-tive Lempel-Ziv coding.See also data compression; file compres-sion; PKZip; WinZip; ZIP file.Compression Control Protocol Ab-breviated CCP. A protocol used with Point-to-Point Protocol (PPP) to configure, en-able, and disable data compression algo-rithms at both ends of the point-to-pointconnection. CCP can support differentcompressionalgorithmsineachdirectionofthe connection.See also Point-to-Point Protocol.CompuServe Abbreviated CIS. A majorprovider of online services including e-mail,file downloading, forums on a variety of top-ics, chat rooms, and Internet access, as wellas commercial services offered to a largenumber of business users. In 1998, Compu-Serve was bought by America Online.For more information on CompuServe, bound A condition inwhich the speed of operation of the proces-sor actually limits the speed of program ex-ecution. The processor is limited by thenumber of arithmetic operations it canperform.See also input/output account In Microsoft Win-dows 2000, an object in the Security Ac-counts Manager that describes a specificcomputer within a network domain. Acomputer account is added for each nodeadded to the domain.Computer Associates InternationalAbbreviated CAI. A leading supplier of en-terprise applications and services to the cor-porateworld,includingdefensecontractorsand Fortune 500 companies.CAI’s rapid expansion in recent years hasbeen due to an aggressive acquisitions pol-icy that has led to the incorporation ofLegent and Cheyenne Software and to ajoint venture with Fujitsu that created theobject-oriented database Jasmine.CAI currently enjoys success with UnicenterTNG, a collection of applications and toolsused to manage enterprise computing.For more information on CAI, Emergency ResponseTeam Abbreviated CERT. Founded in1988 at Carnegie-Mellon University,CERT works with the Internet communityto increase awareness of security issues; itconducts research into improving existingsystems and provides 24-hour technical as-sistance service for responding to securityincidents.Computer Management In MicrosoftWindows 2000, the administrative toolused to manage a local or remote computer.Computer Management is a MicrosoftManagement Console (MMC) snap-in andreplaces several Windows NT administra-tive tools, including Server Manager, UserManager for Domains, and Disk Adminis-trator.See also Active Directory; Microsoft Man-agement Console; snap-in.2461book Page 84 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 90. 85concurrent licensecomputer name 1. In Microsoft Win-dows NT, a name of up to 15 uppercase let-ters that identifies a specific computer to theother computers on the network. The com-puter name is created during installationand must be unique within the workgroupor domain; you can change the computername using the Network applet in ControlPanel.2. In NetBIOS, a name of up to 15 char-acters that uniquely identifies a worksta-tion to computers and users. Once acomputer is named, NetBIOS can establishsessions between computers and use thoselinks to exchange data between systems.These exchanges can be either NetBIOSrequests or Server Message Block (SMB)data. Network applications use NetBIOSnames to locate resources, although theWindows Sockets API is now more com-monly used.See also NetBIOS; WinSock.Computer object In NetWare DirectoryServices, a leaf object representing a comput-er on the network. The Computer object’sproperties can contain information such asthe computer’s physical serial number andthe name of the person to whom the com-puter is currently assigned.See also leaf object; Novell DirectoryServices.Computer Systems Research GroupAbbreviated CSRG. The University of Cal-ifornia, Berkeley, group responsible for thedevelopment of the Berkeley Software Dis-tribution (BSD).CSRG was home to some remarkable pro-grammers over the years and introducedinto Unix many of the fundamental featureswe take for granted. The last BSD release,4.4BSD, was made during 1993, and thegroup was disbanded shortly afterward.concentrator A repeater or hub thatjoins communications channels from sever-al network nodes. Concentrators are notjust simple wire-concentration centers, butalso provide bridging, routing, and othermanagement functions.concurrent Whentwoormoreprograms(processes) have access to the processor atthe same time and must share the system re-sources, they are said to be “running con-currently.” Because a computer canperform operations so quickly, the process-es seem to be occurring at the same time, al-though actually they are not.See also multiprocessing; task; taskswitching; thread.concurrent license A software licensethat allows more than one person at a com-pany to share an application over a net-work, providing that, at any given time,only one person is using it.Different versions of concurrent licensingallow a fixed number of people in an officeto share one copy of an application and al-low the application to be used on both desk-top and portable PCs, rather than run onlyfrom the file server.See also application metering.2461book Page 85 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 91. CONFIG.SYS86CONFIG.SYS In MS-DOS and OS/2, aspecial text file containing settings that con-trol the way the operating system works.In MS-DOS, the CONFIG.SYS file may con-tain 10 to 20 lines of entries. In OS/2, it islikely to contain between 70 and 100 lines ofconfiguration information. CONFIG.SYSmust be in the root directory of the defaultboot disk, normally drive C, and is read onceas the system starts running.configuration The process of establish-ing your own preferred setup for an appli-cation, expansion board, computer system,or network. Most current software can es-tablish a configuration for you automati-cally, although you may need to adjust thatconfiguration to get the best results.See also Desktop Management Interface;Plug and Play.configuration file A file, created by anapplication or an operating system, con-taining configuration information specificto your own computing environment. Ap-plication configuration files may have a file-name extension of CFG or SET; Windowsconfiguration files use the INI filenameextension.If you accidentally erase an application’sconfiguration file, the program will returnto using its default settings. Although theprogram will continue to function, its con-figuration settings may not be suitable foryour system.See also AUTOEXEC.BAT; CONFIG.SYS;NET.CFG.configuration management A termcovering a wide range of networkadministration tasks, often performed bythe network administrator, including:IMaintaining a hardware database contain-ing details of routers, bridges, and connec-tions so that changes in the network can bemade quickly in the event of a failureIAdding and removing workstations andusers to the network as neededIAdding and configuring new servers andcabling systems as the network expandsSee also Desktop Management Interface.configuration register A 16-bit, user-configurable value that determines how aCisco router functions during router initial-ization. You can configure information inhardware by using jumpers and in softwareby specifying a hexadecimal number in con-figuration commands.congestion An excessive amount of traf-fic on the network, causing messages to beblocked for long periods of time and ad-versely affecting network performance.You may see a very slow response from aserver, or you may see an error message tell-ing you that no ports are available at thepresent time for the service or host you arerequesting.See also Ethernet meltdown.connectionless A protocol in which thesource and destination addresses are in-cluded inside each packet so that a directconnection between sender and receiver oran established session between nodes is notrequired for communications. In a connec-tionless service, data packets may not reachtheir destination in the same order in which2461book Page 86 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 92. 87connection speedthey were sent. UDP is a connectionlesstransport service.See also connection-oriented; User Data-gram Protocol.Connectionless Network ProtocolAbbreviated CLNP. An Open Systems In-terconnect (OSI) protocol that provides theOSI Connectionless Network Service forthe delivery of data. It uses datagrams thatinclude addressing information to routenetwork messages. CLNP is used for LANsrather than WANs. CLNP is the OSI equiv-alent of IP (Internet Protocol).See also Connection-Oriented NetworkService.Connectionless Transport ProtocolAbbreviated CLTP. An Open Systems In-terconnect (OSI) protocol that providesend-to-end transport data addressing anderror correction, but does not guarantee de-livery or provide any flow control. CLTP isthe OSI equivalent of UDP.See also Connection-Oriented NetworkService; User Datagram Protocol.Connection Admission Control Ab-breviated CAC. An Asynchronous TransferMode (ATM) function that determineswhether a virtual circuit connection requestwill be accepted.See also Asynchronous Transfer Mode.connection number Anumberassignedto a workstation that attaches to a server; itmay be a different number each time theworkstation attaches. Connection numbersare also assigned to print servers, as well asother applications and processes that usethe server connections.connection-oriented A term used to de-scribe a communications model that goesthrough three well-defined stages: estab-lishing the connection, transferring the da-ta, and releasing the connection. Analogousto a voice telephone call. In a connection-oriented service, data packets always reachtheir destination in the same order in whichthey were sent. TCP is a connection-orient-ed transport service.See also connectionless; TransmissionControl Protocol.Connection-Oriented NetworkService Abbreviated CONS. A datatransmission service in which data is onlytransmitted once a connection has been es-tablished. Asynchronous Transfer Mode(ATM) is a connection-oriented service.See also Connectionless Network Proto-col; Connectionless Transport Protocol.connection speed The speed of a datacommunications circuit. Some circuits aresymmetrical and can maintain the samespeed in both directions; others are asym-metrical and use a faster speed in one direc-tion,usuallythedownstreamside.TableC.1compares the connection speeds availablefor several technologies.See also Asymmetric Digital SubscriberLine; cable modem; High-Bit-Rate DigitalSubscriber Line; Integrated Services Digi-tal Network; modem; Single-Line DigitalSubscriberLine;Very-High-Bit-RateDigitalSubscriber Line.2461book Page 87 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 93. connectivity88connectivity The degree to which anygiven computer or application can cooper-ate with other network components pur-chased from other vendors, in a networkenvironment in which resources are shared.connect time The period of time duringwhich a user is logged on to the network.ConnectView An application with agraphical user interface used to manageNetWare Connect and Novell Internet Ac-cess Server (NIAS) communication servers.CONS See Connection-Oriented Net-work Service.cons See console.Conseil Européen pour la ResearcheNucléaire Abbreviated CERN. The Eu-ropean Laboratory for Particle Physics lo-cated in Geneva, Switzerland, where TimBerners-Lee and associates created the com-municationsprotocolsthatledtotheWorldWide Web.For more information on CERN, Sometimes abbreviated cons.The monitor and keyboard from which theserver or host computer activity can bemonitored.Certain operating system commands andutilities must be executed from the consoleTABLE C.1 CONNECTION SPEEDSTechnology Speed Distance LimitationConventionalmodem56Kbps downstream, up to33.6Kbps upstreamNoneISDN Up to 128Kbps symmetric 18,000 ftCable modem Up to 30Mbps downstream, to10Mbps upstream30 miADSL 1.5 to 8Mbps downstream, to1.544Mbps upstream18,000 ftSDSL 1.544 to 2.048Mbps symmetric 10,000 ftHDSL 1.544 to 2.048Mbps symmetric(over 3 phone lines)15,000 ftVDSL 13 to 52Mbps downstream, 1.5 to2.3Mbps upstream4,500 ft2461book Page 88 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 94. 89container administratordevice; they will not operate from a work-station. In some systems, the console is avirtual device that can be invoked from anyworkstation by a network administratorwith the appropriate rights and privileges.constant angular velocity Abbreviat-ed CAV. An unchanging speed of rotation.Hard disks use a CAV encoding scheme.The constant rate of rotation means thatsectors on the disk are at the maximum den-sity along the inside track of the disk. As theread/write heads move outward, the sectorsmust spread out to cover the increased trackcircumference, and therefore the data-transfer rate falls off.See also constant linear velocity.Constant Bit Rate Abbreviated CBR. Atype of Asynchronous Transfer Mode(ATM) service reserved for voice or videoor other data that must be transmitted at aconstant rate and are intolerant of data loss.See also Asynchronous Transfer Mode;Available Bit Rate; Unspecified Bit Rate;Variable Bit Rate.constant linear velocity AbbreviatedCLV. A changing speed of rotation. CD-ROM disk drives use a CLV encodingscheme to make sure that the data densityremains constant. Information on a com-pact disc is stored in a single, spiral track,divided into many equal-length segments.To read the data, the CD-ROM disk drivemust increase the rotational speed as theread head gets closer to the center of the discand decrease as the head moves back out.See also constant angular velocity.Consultative Committee for Interna-tional Telephony and Telegraphy Ab-breviated CCITT. An organization based inGeneva that develops worldwide data com-munications standards. Three main sets ofstandards have been established:ICCITT Groups 1–4 standards apply tofacsimile transmissions.ICCITT V series of standards apply to mo-dems and error detection and correctionmethods.ICCITT X series standards apply to LANs.Recommendations are published every fouryears. In 1993, after a reorganization, thename was changed to International Tele-communication Union (ITU), and eventhough ITU now creates recommendationsand standards, you will still hear the CCITTstandards mentioned.Seealso InternationalTelecommunicationUnion.container One of the Java programminglanguage classes that can contain graphicaluser interface components. Components ina container usually appear within theboundaries of that container. For example,the classes Dialog, Frame, and Window areall containers.See also Java.container administrator In Novell Di-rectory Services, an administrator who isgranted rights to a container object and allthe objects that the container holds. A con-tainer administrator can be exclusive, indi-cating that no other administrator isallowed access to that container.See also container object; leaf object.2461book Page 89 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 95. container object90container object In Novell DirectoryServices, an object that can contain otherobjects and that is used to represent a logi-cal or physical organizational element with-in a company, such as a department or adivision. The Tree, Country, Organization,and Organizational Unit objects are all con-tainer objects.See also container administrator; Countryobject; leaf object; Organization object; Or-ganizational Unit object; Tree object.container security equivalence Seeimplied security equivalence.contention The competition betweentransmitting nodes for access to communi-cations lines or network resources. The firstdevice to gain access to a channel takes con-trol of the channel. In the event of a colli-sion, when two nodes attempt to transmitat the same time, some arbitration schememust be invoked.See also Carrier Sense Multiple Access/Collision Detection; token passing.context In Novell Directory Services, anobject’s location within the Directory tree.The context is the full path to the containerobject in which the object is placed. If anobject is moved from one container to an-other, it has changed contexts.See also container object; leaf object.context switching Switching from oneprogram to another without ending the firstprogram. Context switching allows you tooperate several programs at the same time;but it differs from true multitasking in thatwhen you are using one program, all theother programs loaded onto your systemmust halt.control character A nonprinting char-acter with a special meaning.Control characters, such as Carriage Re-turn, Line Feed, Bell, or Escape, perform aspecific operation on a terminal, printer, orcommunications line. They are grouped to-gether as the first 32 characters in the ASCIIcharacter set; see Appendix C for details.You can type a control character from thekeyboard by pressing and holding the Ctrlkey while you simultaneously press anoth-er key. For example, if you press and holdthe Ctrl key and then press C, you generateCtrl+C, also known as Break. Controlcharacter sequences are often used insideapplication programs as menu commandshortcuts.See also American Standard Code forInformation Interchange; ExtendedBinary Coded Decimal Interchange Code;Unicode.control code A sequence of one or morecharacters used for hardware control; alsoknown as setup strings or escape sequences.Control codes are used with printers, mo-dems, and displays. Printer control codesoften begin with an escape character, fol-lowed by one or more characters that theprinter interprets as commands it must per-form rather than as text it must print.Control Panel InMicrosoftWindows,aspecial system folder that contains appletsused to look at or change configuration in-formation. Each applet manages a singletask such as adding or removing a program2461book Page 90 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 96. 91cooperative multitaskingfrom your system, setting up a connectionto the Internet, or changing display settings.See also Network and Dial-upConnections.Controlled Access Unit AbbreviatedCAU. An intelligent Multistation AccessUnit (MAU) or multiport wiring hub for atoken-ring network that allows ports to beswitched on and off.controllerless modem A modem thatshifts all the protocol management, error de-tection and correction, and data compres-sion onto software running on the system’sCPU. This allows the modem manufacturerto make a much cheaper modem that doesnot require the memory or processing powerofatraditionalmodem.Alsoknownasasoftmodem.control set That portion of the Micro-soft Windows Registry that contains infor-mation required to boot the operating sys-tem and restore the last known goodconfiguration.conventional memory The amount ofmemory accessible by MS-DOS in PCs usingan Intel processor operating in real mode;normally the first 640KB.The designers of the original IBM PC made640KB available to the operating systemand applications and reserved the remain-ing space for internal system use, the BIOS,and video buffers. Although 640KB maynot seem like much memory space now, itwas ten times the amount of memory avail-able in other leading personal computersavailable at the time. Since then, applica-tions have increased in size to the point that640KB is inadequate.See also expanded memory; extendedmemory; high memory area; memorymanagement; protected mode.convergence The synchronization pro-cess that a network must go through imme-diately after a routing change takes place onthe network. Convergence time is the timerequired to update all the routers on the net-work with routing information changes.See also routing table.convergence sublayer Abbreviated CS.OneoftwosublayersthatmakeuptheATMAdaptation Layer; the other being the seg-mentation and reassembly sublayer (SAR).The convergence sublayer is the upper layerthat provides the interface for the variousATM services, pads the cells, and addsheaders and trailers before passing the cellto the SAR.See also ATM Adaptation Layer; segmen-tation and reassembly sublayer.cookie 1. A block of data sent from aserver to a client in response to a request bythe client.2. On the World Wide Web, a block of datastored by the server on the system runningthe browser or client software, which canbe retrieved by the server during a futuresession. A cookie contains information thatcan identify the user for administrative rea-sons or to prepare a custom Web page.cooperative multitasking A form ofmultitasking in which all running applica-tions must work together to share systemresources.2461book Page 91 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 97. Copper Distributed Data Interface92The operating system supports cooperativemultitasking by maintaining a list of the ac-tive applications and the order in which theyexecute. When control is transferred to anapplication, the other applications cannotrun until that application returns controlback to the operating system once again.A cooperative multitasking system differsfrom a preemptive multitasking system, inwhich the operating system executes eachapplication in turn for a specific period oftime (depending on priority) before switch-ing to the next application, regardless ofwhether the applications themselves returncontrol to the operating system.See also context switching; time-slicemultitasking.Copper Distributed Data InterfaceAbbreviated CDDI. A version of the FDDIstandard designed to run on shielded andunshielded twisted-pair cable rather thanon fiber-optic cable. CDDI is capable of100Mbps data transfer rates.See also Fiber Distributed Data Interface.coprocessor A secondary processorused to speed up operations by taking overa specific part of the main processor’s work.The most common type of coprocessor isthe math, or floating-point, coprocessor,which is designed to manage arithmetic cal-culations many times faster than does themain processor.copy left The copyright or General Pub-lic License of the Free Software Foundation(FSF), which states that any of the softwaredeveloped using free software from the FSFmust be distributed to others withoutcharge.See also open source software.CORBA See Common Object RequestBroker Architecture.COSE See Common Open SoftwareEnvironment.counter log In Microsoft Windows2000, a System Monitor log used to moni-tor data from local or remote computersabout hardware use and system service ac-tivity.See also alert log; System Monitor; tracelog.Country object In Novell Directory Ser-vices, a container object placed directly un-der the Root object in the Directory treethat defines the country for a specific part ofyour network. Country object names aredefined by the International Organizationfor Standardization (ISO) and follow astandard naming convention. You mustspecify the Country object if you want toconnect to external networks using X.500directory services.CPDA See Certified PowerBuilder De-veloper Associate.CPDP See Certified PowerBuilder De-veloper Professional.CPE See customer-premisesequipment.CPI-C See Common Programming In-terface for Communications.cps See characters per second.2461book Page 92 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 98. 93Ctrl+Alt+DelCPTS See Certified Performance andTuning Specialist.CPU See central processing unit.cracker An unauthorized person whobreaks into a computer system planning todo harm or damage or with criminal intent.The popular press often portrays crackersas people with exceptional talent for elud-ing detection, and some of them are, butmost of them use a set of well-worn tricks toexploit common security weaknesses in thesystems they target.See also attack; hacker; intruder.crash An unexpected program halt, some-times due to a hardware failure but most of-tenduetoasoftwareerror,fromwhichthereis no recovery. You usually need to rebootthe computer to recover after a crash.See also blue screen of death.CRC See cyclical redundancy check.critical error An error in a program thatforces the program to stop until the usercorrects the error condition. Examples ofthis kind of error are attempts to write to afloppy disk when there is no disk in thedrive or to print to a printer that has run outof paper.crosstalk In communications, any inter-ference from a physically adjacent channelthat corrupts the signal and causes trans-mission errors.See also far-end crosstalk; near-endcrosstalk.Cryptography API Abbreviated CAPI.An API first introduced in MicrosoftWindows NT 4 that provides encryptionand decryption functions for applicationdevelopers.CS See convergence sublayer.CSE See Certified Solutions Expert.C shell In Unix, a popular command in-terpreter; pronounced “sea shell.”Developed at the University of California atBerkeley as part of the BSD development asan alternative to the Bourne shell. In addi-tion to the features found in the Bourneshell, the C shell adds integer arithmetic, ahistory mechanism that can recall past com-mands in whole or in part, aliasing of fre-quently used commands, job control, and abuilt-in set of operators based on the C pro-gramming language used for writing shellscripts.See also Bash; Bourne shell; Korn shell;Linux; Unix shell.CSMA/CD See Carrier Sense MultipleAccess/Collision Detection.CSRG See Computer Systems Re-search Group.CSU See Channel Service Unit.Ctrl+Alt+Del A three-key combinationused to reset the machine and reload the op-erating system. By pressing Ctrl+Alt+Del,you initiate a warm boot, which restarts thecomputer without going through the pow-er-on self tests (POSTs) normally run whenthe computer goes through a cold boot.In Windows 98 and 2000, the sequenceopens a dialog box from which you caneither end a task or shut down the2461book Page 93 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 99. Ctrl+Break94computer. Sometimes called the three-finger salute.See also warm boot.Ctrl+Break See Ctrl+C.Ctrl+C 1. A key combination recognizedby Unix, MS-DOS, and other operating sys-tems as a user-initiated interruption. Press-ing Ctrl+C stops a batch file, macro, orcommand (for example, a directory listing,a search, or a sort).2. A keyboard shortcut recognized bymany programs as the instruction to copythe selected item.Ctrl key A key on the keyboard that,when pressed at the same time as anotherkey, generates a nonprinting controlcharacter.On some keyboards, this key is labeledControl rather than Ctrl, but it producesthe same function.CTS See Clear to Send.CUE See Certified Unicenter Engineer.current directory In many operatingsystems, the directory that will be searchedfirst for any file you request, and the direc-tory in which any new files will be stored(unless you specifically designate anotherdirectory). The current directory is not thesame as the default directory, which is thedirectory that an application uses unlessyou specify another.See also dot; dot dot; period and double-period directories.current drive In many operating sys-tems, the disk drive that is being used forreading and writing files. The current driveis not the same as the default drive, which isthe drive that an application uses unless youspecify another.See also drive mapping.cursor A special character displayed on amonitor to indicate where the next charac-ter will appear when it is typed. In text orcharacter mode, the cursor is usually ablinking rectangle or underline. In a graph-ical user interface, the mouse cursor cantakemanyshapes,dependingonthecurrentoperation and its screen location.cursor-movement keys The keys onthe keyboard that move the cursor; alsocalled cursor-control keys. These keys in-clude the four labeled with arrows and theHome, Pg Up, End, and Pg Dn keys.On full-size keyboards, cursor-movementkeys are often found on the numeric key-pad; laptops and notebooks often have sep-arate cursor-movement keys.CU-SeeMe Apopularvideoconferencingand videophone product that works overthe Internet.CU-SeeMe was originally developed atCornell University and is available free forthe PC and the Macintosh. An enhancedcommercial version that adds an electronicchalkboard is available from White PineSoftware. The software is designed for per-sonal use and for use in instruction and inbusiness communications.See also White Pine Software.2461book Page 94 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 100. 95CyrixCustomer Information ControlSystem Abbreviated CICS. An IBM-mainframe client/server program that man-ages transaction processing in IBM’s VMand MVS operating systems and that is scal-able to thousands of users. It also providespassword security, transaction logging forbackup and recovery, and an activity logthat can be used to analyze session perfor-mance, as well as facilities for creating, us-ing, and maintaining databases.customer-premises equipment Ab-breviated CPE. Communications equip-ment, either leased or owned, used at acustomer site.cut through A technique used by someEthernet hardware to speed up packet for-warding. Only the first few bytes of thepacket are examined before it is forwardedor filtered. This process is much faster thanlooking at the whole packet, but it does al-low some bad packets to be forwarded.See also store-and-forward.cut-through switching Atypeofswitch-ing used on a Token Ring network in whichdata is forwarded as soon as the first 20 or 30bytes in a data frame have been read.After the header information has been read,the connection is established between inputand output ports, and the transmission be-gins immediately. Sometimes known as on-the-fly switching.See also store-and-forward.CxBus See Cisco Extended Bus.cyclical redundancy check Abbreviat-ed CRC. A complex calculation methodused to check the accuracy of a digital trans-mission over a communications link or toensure the integrity of a file stored on a harddisk.The sending computer uses one of severalformulas to calculate a value from theinformation contained in the data, and thisvalue is appended to the message block be-fore it is sent. The receiving computer per-forms the same calculation on the samedata and compares this number with thereceived CRC. If the two CRCs do notmatch, indicating a transmission error, thereceiving computer asks the sending com-puter to retransmit the data.This procedure is known as a redundancycheck because each transmission includesextra or redundant error-checking values aswell as the data itself.As a security check, a CRC may be used tocompare the current size of an executablefile against the original size to determine ifthe file has been tampered with or changedin some way.See also checksum; Kermit; Xmodem;Ymodem; Zmodem.Cyrix A designer of microprocessors, in-cluding clones of popular Intel chips such asthe 6x86MX and the MII (pronounced M-two). Cyrix was bought by National Semi-conductor in 1998.For more information about Cyrix, also Advanced Micro Devices, Inc.;Pentium; Pentium II; Pentium III.2461book Page 95 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 101. DACL96DDACL See Discretionary Access ControlList.daemon Pronounced “dee-mon.” Abackground program that runs unattendedand is usually invisible to the user, provid-ing important system services.Daemons manage all sorts of tasks, includ-ing e-mail, networking, and Internetservices. Some daemons are triggered au-tomatically by events to perform theirwork; others operate at timed intervals.Because daemons spend so much of theirtime idle, waiting for something to hap-pen, they do not consume large amounts ofsystem resources.DAP See Directory Access Protocol.DAS See dual-attached station.DAT See digital audio Information in a form suitable forprocessing by a computer, such as the digi-tal representation of text, numbers, graphicimages, or sounds. Strictly speaking, data isthe plural of the Latin word datum, mean-ing an item of information; but the term iscommonly used in both plural and singularconstructions.database A collection of related objects,includingtables,forms,reports,queries,andscripts, created and organized by a databasemanagement system (DBMS). A databasecan contain information of almost any type,such as a list of magazine subscribers,personal data on the space shuttle astro-nauts, or a collection of graphical imagesand video clips.See also database management system;database model; table.database management system Ab-breviated DBMS. Software that controlsthe data in a database, including overall or-ganization, storage, retrieval, security, anddata integrity. A DBMS can also format re-ports for printed output and can import andexport data from other applications usingstandard file formats. A data-manipulationlanguage is usually provided to supportdatabase queries.See also database; database model; querylanguage.database model The method used by adatabase management system (DBMS) toorganize the structure of the database. Themost common database model is the rela-tional database.See also relational database.database server Any database applica-tion that follows the client/server architec-ture model, which divides the applicationinto two parts: a front-end running on theuser’s workstation and a back-end runningon a server or host computer. The front-endinteracts with the user and collects and dis-plays the data. The back-end performs all2461book Page 96 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 102. 97Data Encryption Standardthe computer-intensive tasks, includingdata analysis, storage, and manipulation.Database Specialist: Informix DynamicServer A certification from Informix de-signed for computer professionals who im-plement and manage Informix DynamicServer databases. The associated exams cov-er relational database design, StructuredQuery Language (SQL), and managementand optimization of Informix Dynamic Serv-er databases.See also Informix-4GL Certified Profes-sional; system bits In asynchronous transmis-sions, the bits that actually make up the da-ta. Usually, seven or eight data bits aregrouped together. Each group of data bitsin a transmission is preceded by a start bitand followed by an optional parity bit aswell as one or more stop bits.See also communications parameters;parity; start bit; stop bit(s).Data Carrier Detect Abbreviated DCD.A hardware signal defined by the RS-232-Cstandard that indicates that the device,usually a modem, is online and ready communication The transfer ofinformation from one computer to anotherover a communications link. The transfercan be occasional, continuous, or a combi-nation of communications equipmentAbbreviated DCE. In communications, anydevice that connects a computer or terminalto a communications channel or public net-work; usually a modem.See also data terminal compression Any method of en-coding data so that it occupies less spacethan it did in its original form, thus allow-ing that data to be stored, backed up, re-trieved, or transmitted more efficiently.Data compression is used in fax and manyother forms of data transmission, CD-ROM publishing, still-image and video-im-age manipulation, and database manage-ment systems.See also Huffman coding; Joint Photo-graphic Experts Group; lossless compres-sion; lossy compression; Moving PicturesExperts connector (Type 1) A connectorfor use with Type 1 cable, designed by IBMfor use in Token Ring network scheme The methodused by a hard-disk controller to store infor-mation onto a hard disk or a floppy disk.Common encoding schemes include therun-length limited (RLL) and advanced run-length limited (ARLL) methods.See also advanced run-length limited en-coding; RLL encoding.Data Encryption Standard Abbreviat-ed DES. A standard method of encryptingand decrypting data, developed by the U.S.National Bureau of Standards. DES worksby a combination of transposition and sub-stitution. It is used by the federal govern-ment and most banks and money-transfer2461book Page 97 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 103. data file98systems to protect all sensitive computerinformation.See also encryption; Pretty Good file A file that contains informa-tion—text, graphics, or numbers—ratherthan executable program code.datagram A message unit that containssource and destination address informa-tion, as well as the data itself, which is rout-ed through a packet-switching network.The data held in the datagram is often re-ferred to as the payload, and the addressinginformation is usually contained in theheader. Because the destination address iscontained in all datagrams, they do nothave to arrive in consecutive order. Data-gramsarecommonlyusedinconnectionlesstransmission systems. IP (Internet Protocol)and IPX (Internetwork Packet Exchange)are both datagram services.See also frame; data packet.Datagram Delivery Protocol Abbrevi-ated DDP. A routing protocol developed byApple Computer as a part of its layer The second of seven lay-ers of the OSI Reference Model for comput-er-to-computer communications. The data-link layer validates the integrity of the flowof data from one node to another by syn-chronizing blocks of data and controllingthe flow of data.The Institute of Electrical and ElectronicEngineers (IEEE) has divided the data-linklayer into two other layers—the logical linkcontrol (LLC) layer sits above the media ac-cess control (MAC) layer.See also OSI Reference Model.Data Link Switching AbbreviatedDLSw. A standard for encapsulating or tun-neling IBM Systems Network Architecture(SNA) and NetBIOS applications across IPnetworks.See also Advanced Peer-to-Peer Network-ing; Systems Network mining The process of displayinghistorical commercial data in a multidimen-sional form so that previously hidden rela-tionships are exposed through the use ofadvanced statistical tools, making themeasier to group and summarize.See also data warehousing; online ana-lytical processing; online packet One unit of informationtransmitted as a discrete entity from onenode on the network to another. More spe-cifically, a packet is a transmission unit of afixed maximum length that contains aheader with the destination address, a set ofdata, and error control information.See also processing Abbreviated DP. Alsocalled electronic data processing (EDP). Aterm used to describe work done by mini-computers and mainframe computers in adata center or business protection Techniques used bynetwork operating systems to ensure the in-tegrity of data on the network, including2461book Page 98 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 104. 99DB connectorprotecting data against surface defects de-veloping on the disk and storing redundantcopies of important system data, such as fileindices and file allocation tables (FATs).Disk duplexing, disk mirroring, a wellthought out backup scheme, and RAIDtechniques all provide different levels ofdata protection.See also diskless workstation; disk strip-ing; disk striping with parity; fault toler-ance; Hot Fix; intruder; redundant array ofinexpensive disks; virus.Data Service Unit Abbreviated DSU. Adevice that connects DTE (data terminalequipment) to digital communicationslines. A DSU formats the data for transmis-sion on the public carrier WANs and en-sures that the carrier’s requirements fordata formats are met.See also Channel Service Unit.Data Set Ready Abbreviated DSR. Ahardware signal defined by the RS-232-Cstandard to indicate that the device is readyto operate.See also Clear to terminal equipment AbbreviatedDTE. In communications, any device, suchas a terminal or a computer, connected to acommunications device, channel, or publicnetwork.See also data communications equipment.Data Terminal Ready AbbreviatedDTR. A hardware signal defined by theRS-232-C standard sent from a computerto a modem to indicate that the computeris ready to receive a rate 1. The speed atwhich a disk drive can transfer informationfrom the drive to the processor, usually mea-sured in megabits or megabytes per second.2. The rate of information exchange be-tween two systems. For example, an Ether-net LAN may achieve 10Mbps, and a FiberDistributed Data Interface (FDDI) systemmay reach 100Mbps.See also connection warehousing A method of storingvery large amounts of data, usually histor-ical transaction processing data, for lateranalysis and reporting.The data warehouse is accessed by softwarecapable of extracting trends from the rawdata and creating comparative reports.See also data mining.dB See decibel.DB connector Any of several types of ca-ble connectors used for parallel or serial ca-bles. The number following the letters DB(for data bus) indicates the number of pinsthat the connector usually has; a DB-25connector can have a maximum of 25 pins,and a DB-9 connector can have as many as9. In practice, not all the pins (and not allthe lines in the cable) may be present in thelarger connectors. If your situation de-mands that all the lines be present, makesure you buy the right cable. Common DBconnectors include the following:IDB-9 Defined by the RS-449 standardas well as the ISO (International Organi-zation for Standardization).2461book Page 99 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 105. DBCS100IDB-25 A standard connector used withRS-232-C wiring, with 25 pins (13 on thetop row and 12 on the bottom).IDB-37 Defined as the RS-449 primarychannel connector.DB-15, DB-19, and DB-50 connectors arealso available. The accompanying illustra-tion shows a male and female DB-25connector.DB CONNECTORDBCS See double-byte character set.DBMS See database managementsystem.DC-2000 Aquarter-inchtapeminicartridgeused in some tape backup systems. DC-2000has a capacity of up to 250MB when someform of data compression is used.See also quarter-inch cartridge.DCD See Data Carrier Detect.DCE See data communicationsequipment.DCE See Distributed ComputingEnvironment.D channel The channel in ISDN that isused for control signals and customer data.In the Base Rate ISDN (BRI), the D channeloperates at 16Kbps; in the Primary RateISDN (PRI), it operates at 64Kbps.DCOM See Distributed ComponentObject Model.DCPROMO InMicrosoftWindows2000Server, the Active Directory InstallationWizard that promotes a member server orstand-alone server to a domain controller.When run on a domain controller, this pro-gram can demote the computer to a mem-ber server or a stand-alone server.DDCMP See Digital Data Communica-tions Message Protocol.DDD See direct distance dialing.DDE See Dynamic Data Exchange.2461book Page 100 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 106. 101dedicated circuitDDNS See Dynamic DNS.DDP See Datagram Delivery Protocol.deadlock An error condition or stale-mate that occurs when two programs or de-vices are each waiting for a signal from theother before they can continue.DEC See Digital Equipment Corporation.DEC Alpha Also called the DEC AlphaAXP or the DECchip 21264. A 64-bit,RISC (reduced instruction set computing)microprocessor from Digital EquipmentCorporation (DEC), first introduced in1992.The Alpha is a superscalar, superpipelineddesign, which allows the processor to exe-cute more than one instruction per clockcycle; it can execute as many as six instruc-tions per clock cycle and can sustain fourinstructions per clock cycle.It has data and instruction caches, a float-ing-point processor, 64-bit registers, 64-bitdata and address buses, and a 128-bit datapath between the processor and memory.The internal architecture is symmetricalmultiprocessing(SMP)compliant,meaningthat it can be used in multiprocessing con-figurations. The chip is available in severalmodels with operating frequencies in the300 to 700MHz range; a 1GHz model is ex-pected by the year 2000.decapsulation A process used in net-working in which the receiving systemlooks at the header of an arriving messageto determine if the message contains data. Ifthe message does contain data, the header isremoved and the data decoded.See also encapsulation.decibel Abbreviated dB. One-tenth of abel, a unit of measurement common in elec-tronics that quantifies the loudness orstrength of a signal. A decibel is a relativemeasurement derived by comparing a mea-sured level against a known reference.decimal The base-10 numbering systemthat uses the familiar numbers 0–9; alsoknown as the base 10 radix or the decimalradix.See also binary; hexadecimal.decimal radix See decimal.DECnet A series of communications andnetworking products from Digital Equip-ment Corporation (DEC). DECnet is com-patible with Ethernet, as well as withWANs using baseband and broadband pri-vate and public communications channels.DECnet is built into the VAX VMS operat-ing system.See also Digital Network Architecture.decode 1. To decompress a video file af-ter receipt so that you can view it. Most de-coding is done by the client browser.2. To convert coded data back into its orig-inal form, usually as readable text.See also codec; decryption; encode;uuencode.decryption The process of convertingencrypted data back into its original form.See also encryption.dedicated circuit See dedicated line;direct connection.2461book Page 101 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 107. dedicated line102dedicated line A communications cir-cuit used for one specific purpose and notused by or shared between other users. Youneed only dial a dedicated line to restoreservice after an unscheduled interruption.Also known as a dedicated circuit.See also leased line.dedicated router A router that performsno functions other than routing tasks.dedicated server A computer on thenetwork that functions only as a server per-forming specific networking tasks, such asstoring files, printing, or managing externalcommunications.Dedicated Token Ring An IEEE 802.5rToken Ring specification that allows forfull-duplex connections at a speed of up to32Mbps. By enabling full-duplex commu-nications, the token-passing mechanism isnot used, and communications can takeplace between a device and a switch at anytime.See also 802.x; token-ring network.default A standard setting, used until analternative is chosen. The default server isthe first server that you log on to. The de-fault drive is the drive that a workstation iscurrently using.A default is usually a relatively safe courseof action to try first; many programs pro-vide defaults you can use until you knowenough about the program to specify yourown settings.default directory A standard directoryor set of directories used by the operatingsystem or by an application.Some operating systems create several de-fault directories when the file system is cre-ated. For example, Novell NetWare createsthe following directories when the SYS vol-ume is created:ISYS:SYSTEM, for the NetWare operatingsystem filesISYS:PUBLIC, for utility and user programsISYS:LOGIN, for programs allowing usersto log in to the serverISYS:MAIL, a directory used by NetWare-compatible electronic-mail applicationsdefault server In Novell NetWare, theserver that responds to the Get NearestServer request made as a user starts thelogon process. Novell Directory Serviceshas replaced the need for the default serverdestination with the default context.See also Context.default shares In Microsoft Windows2000, resources shared by default when theoperating system is first installed.See also common share; hidden share;share; sharing.defense in depth A term borrowedfrom the military used to describe defensivemeasures that reinforce each other, hidingthe defenders activities from view and al-lowing the defender to respond to an attackquickly and effectively.In the network world, defense in depth de-scribes an approach to network securitythat uses several forms of defense against anintruder and that does not rely on one singledefensive mechanism.2461book Page 102 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 108. 103demand pagingdefragmentation The process of reorga-nizing and rewriting files so that they occu-py one large area on a hard disk rather thanseveral smaller areas.When a file on a hard disk is updated, it maybe written into different areas all over thedisk. This outcome is particularly likelywhen the hard disk is continuously updatedover a long period of time. This file frag-mentation can lead to significant delays inloading files, but its effect can be reversedby defragmentation.See also disk optimizer.defragmenter Any utility that rewritesall the parts of a fragmented file into contig-uous areas on a hard disk. A defragmenter(such as the Microsoft Windows 98 utilityDisk Defragmenter) can restore perfor-mance lost because of file fragmentation.See also defragmentation; disk optimizer.delay In communications, a pause in ac-tivity, representing the time during whichtransmission-related resources are unavail-able for relaying a message.See also propagation delay.delay distortion The distortion of a sig-nal caused by the relative difference inspeed of the various components of that sig-nal; in particular, the distortion of the high-frequency component. Also called envelopedelay.delete To remove a file from a disk or toremove an item from a file. Files can be de-leted using operating system commands ordirectly from within an application.When a file is deleted from a disk, the fileis not physically removed; although it ishidden, it is still there on the disk until it isoverwritten. In certain circumstances it ispossible to undelete or recover the originalinformation with utilities designed for thatpurpose. If you find you have deleted animportant file by accident, do not writeany other files to that disk so that you donot overwrite the deleted file. Some net-work operating systems use a delete inhibitattribute to prevent accidental deletions;other operating systems rely on a read-only attribute.delimiter 1. Any special character thatseparates individual items in a data set orfile. For example, in a comma-delimitedfile, the comma is placed between each datavalue as the delimiter.2. In a token-ring network, a delimiter is abit pattern that defines the limits of a frameor token on the network.Dell Computer Corporation Oneoftheworld’s top five PC manufacturers. Dell pi-oneered direct sales of the PC using a con-figure-it-yourself Web site.Best known for PC and laptop sales, Dell isalso pursuing the server market and has re-cently expanded into the enterprise storagemarket with the PowerVault line of SCSI-based storage subsystems, tape backup sys-tems, and scalable disk subsystems.For more information on Dell, paging A common form of vir-tual memory management in which pagesof information are read into memory fromdisk only when required by the program.See also swapping.2461book Page 103 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 109. demand priority104demand priority A technique used in100VG-AnyLAN to arbitrate access to thenetwork and avoid collisions. Demand pri-ority replaces CSMA/CD, which is used inslower Ethernet networks.Demand priority can also prioritize specificnetwork traffic such as video and othertime-critical data, giving it a higher prece-dence; if multiple requests are received, thehighest priority is always serviced first.See also Fast Ethernet.demodulation In communications, theprocess of retrieving the data from amodulated carrier signal; the reverse ofmodulation.See also modem.denial of service attack An attack byan intruder that prevents a computer sys-tem from providing a service.A denial-of-service attack will typically in-volve opening and dropping a large numberof TCP/IP connections very quickly so thatthe target system spends all its time dealingwith the connection overhead to the pointthat it cannot respond to valid user re-quests. Other attacks may exploit knownsoftware security holes to crash servers.A denial-of-service attack is much easier toexecute than an attempt at unauthorizedaccess, because the denial-of-service attacknever actually requires access to the system.See also brute-force attack; dictionary at-tack; mail bombing; social engineering;Trojan Horse.departmental LAN A local-area net-work used by a relatively small group ofpeople working on common tasks; it pro-vides shared local resources, such as print-ers, data, and applications.DES See Data Encryption Standard.descendant key InMicrosoftWindows,all the subkeys that appear when you ex-pand a key in the Windows Registry.See also key; Registry.DeskSet A collection of graphical desk-top applications bundled with Sun Micro-system’s Solaris.DeskSet includes a file manager with op-tions for copying, moving, renaming, anddeleting files, a terminal emulator, text ed-itor, calculator, clock, and calendar, as wellas special programs and utilities.See also Solaris.desktop management The process ofmanaging desktop workstation hardwareand software components automatically,often from a central location.See also total cost of ownership; Zero Ad-ministration for Windows.Desktop Management Interface Ab-breviated DMI. A standard API for identify-ing desktop workstation hardware compo-nents automatically, without interventionfrom the user.At a minimum, DMI identifies the manu-facturer, component name, version, serialnumber (if appropriate), and installationtime and date of any component installed inanetworkedworkstation.Thisinformationis designed to help network administratorsresolve configuration problems quickly and2461book Page 104 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 110. 105device nameeasily and to indicate when and where sys-tem upgrades should be applied. PCs, Mac-intosh computers, and Unix systems are allcovered by DMI.DMI is backed by Digital Equipment Cor-poration (DEC), IBM, Intel, Microsoft, No-vell, Sun, and more than 300 other vendors.See also Plug and Play; total cost of own-ership; Web-based Enterprise Manage-ment; Wired for Management; ZeroAdministration for Windows.desktop video The combination of vid-eo capture hardware and application soft-ware that controls the display of video ortelevision pictures on a desktop PC.Desktop video is becoming increasingly im-portant with the sharp increase in video-conferencing applications now available.destination address The address por-tion of a packet or datagram that identifiesthe intended recipient station.See also source address.destination host A computer system onthe network that is the final destination fora file transfer or for an e-mail message.device A general term used to describeany computer peripheral or hardware ele-ment that can send or receive data.Some examples are modems, printers, serialports, disk drives, routers, bridges, and con-centrators. Some devices require special soft-ware,ordevicedrivers,tocontrolormanagethem; others have built-in intelligence.In Unix and certain other operating systems,all peripherals are treated as though theywere files. When Unix writes information toyour terminal, it is actually writing to a spe-cial file that represents your terminal.See also device driver.device dependence The requirementthat a specific hardware component bepresent for a program to work. Device-de-pendent software is often difficult to moveor port to another computer because of itsreliance on specific hardware.See also device independence.device driver A small program that al-lows a computer to communicate with andcontrol a device. Each operating system con-tains a standard set of device drivers for thekeyboard,themonitor,andsoon.Whenyouadd specialized peripheral devices, such as aCD-ROM disk drive or a network interfacecard, you must install the appropriate devicedriver so that the operating system knowshow to manage the device.See also Plug and Play.device independence The ability toproduce similar results in a variety of envi-ronments, without requiring the presenceof specific hardware.The Java programming language and thePostScript page-description language areexamples of device independence. Java runson a wide range of computers, from the PCto a Cray; PostScript is used by many print-er manufacturers.See also device dependence.device name The name used by theoperating system to identify a computer-system component. For example, COM1 isthe Windows device name for the firstserial port on the PC.2461book Page 105 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 111. device number106device number A unique number as-signed to a device so that it can operate onthe network. Devices are identified by threenumbers:IA physical address set by jumpers on theadapter boardIA device code determined by the physicaladdressIA logical address determined by the orderin which the drivers are loaded and by thephysical address of the adapterSee also Ethernet address; hardwareaddress.Dfs See Distributed file system.DHCP See Dynamic Host ConfigurationProtocol.diagnostic program A program thattests computer hardware and peripheral de-vices for correct operation. Some faults,known as hard faults, are relatively easy tofind, and the diagnostic program will diag-nose them correctly every time. Otherfaults, called soft faults, can be difficult tofind, because they occur under specific cir-cumstances rather than every time thememory location is tested.Most computers run a simple set of systemchecks when the computer is first turnedon. The PC tests are stored in ROM and areknown as power-on self tests (POSTs). If aPOST detects an error condition, the com-puter stops and displays an error messageon the screen.dialback modem See callback modem.dial-in/dial-out server See asynchro-nous communications server.Dialogic Corp A major manufacturer ofhigh-performance telephony products, in-cluding those used in voice, data, fax,speech synthesis, ISDN networking, andcall center management applications.For more information on Dialogic, line A nondedicated communica-tion line in which a connection is estab-lished by dialing the destination code andthen broken when the call is complete.See also dedicated line; leased line.Dial-Up Networking Softwareprovidedwith Microsoft’s Windows products thatallows the clients to dial out and establishPoint-to-Point Protocol (PPP) connections.dictionary attack An attack by an in-truder that checks passwords in a passwordfile against a list of words likely to be usedas passwords. Some versions of this attackcheck the entire language lexicon.See also brute-force attack; denial of ser-vice attack; mail bombing; social engineer-ing; Trojan Horse.differential backup A backup of a harddisk that includes only the information thathas changed since the last complete backup.A differential backup assumes that a fullbackup already exists and that in the eventof an accident, this complete backup willbe restored before the differential backupis reloaded.2461book Page 106 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 112. 107digital signaldifferential SCSI A Small ComputerSystem Interface (SCSI) bus wiring schemethat uses two wires for each signal on thebus. One wire carries the signal, while theother carries its inverse. Differential SCSIminimizes the effects of external interfer-ence and so allows longer SCSI cablelengths to be used.See also single-ended SCSI; Small Com-puter System Interface.digest A collection of Internet mailinglist posts collected together and sent out asa single large message rather than as a num-ber of smaller messages. Using a digest is agood way to cut down on the number ofnoncritical e-mail messages you receive.See also LISTSERV; listserver; mailing Describes any device that repre-sents values in the form of binary digits orbits.See also audio tape Abbreviated DAT. Amethod of recording information in digitalform on a small audio tape cassette, origi-nally developed by Sony and Hewlett-Pack-ard. The most common format is a 4-millimeter, helical-scan drive, which canhold more than 3GB of information. DATscan be used as backup media; however, likeall tape devices, they are relatively slow.Digital Data Communications Mes-sage Protocol Abbreviated DDCMP. Abyte-oriented, link-layer synchronous pro-tocol from Digital Equipment Corporation(DEC), used as the primary data-link com-ponent of DECnet.Digital Equipment Corporation Ab-breviated DEC. A major manufacturer ofminicomputers and mainframe computers,founded in 1957, long recognized for itshigh-quality computer systems. DEC’smost popular product line, the VAX series,ranges from small desktop systems to largemainframes suitable for scientific and com-mercial processing. DEC was bought byCompaq Computer Corporation in 1998.For more information on DEC, also DEC Alpha.Digital Network Architecture Abbre-viated DNA. The framework within whichDigital Equipment Corporation (DEC) de-signs and develops all its service See digital signal Abbreviated DS; alsoknown as digital service. There are severallevels of common carrier digital transmis-sion service:IDS-0 64Kbps.IDS-1 1.544Mbps (T1).IDS-1C Two DS-1 channels are multi-plexed into a single DS-1C 3.152Mbpschannel.IDS-2 Two DS-1C channels are multi-plexed into one DS-2 6.312Mbps (T2)channel.IDS-3 Seven DS-2 channels are multi-plexed into a single 44.736Mbps (T3)channel.IDS-4 Six DS-3 channels are multiplexedinto one 274.176Mbps (T4) DS-4 channel.2461book Page 107 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 113. Digital Signal Processing108The higher-capacity channels are construct-ed by multiplexing the lower-bandwidthchannels together, with some additionalframing and administrative overhead.DS-0 is also referred to as fractional T1,because it bridges the gap between 56-Kbpsdirect dial service (DDS) and a full T1implementation.DIGITAL SIGNALDigital Signal Processing AbbreviatedDSP. An integrated circuit used in high-speeddatamanipulation.YouwillfindDSPchips integrated into sound cards, modems,and video-conferencing hardware for use incommunications, image manipulation, andother data-acquisition applications.See also codec; desktop signature An electronic signa-ture that cannot be forged. A digital signa-ture confirms that the document or e-mailin question originated from the individualor company whose name appears on thedocument and that the document has notbeen altered or tampered with in any waysince it was signed.See also certificate.2461book Page 108 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 114. 109DIP switchDigital Subscriber Line AbbreviatedDSL. A high-speed data transmission tech-nology originally developed by Bellcorethat delivers high bandwidth over existingtwisted-pair copper telephone lines.There are several DSL services, providingdata rates from 16Kbps to 52Mbps. Theservices can be symmetrical, with the samedatarateinbothupstreamanddownstreamdirections, or asymmetrical, with the down-stream capacity greater than the upstreamcapacity. Asymmetric services are particu-larly suitable for Internet users, becausemore information is downloaded than isuploaded.As DSL data rates increase, the distanceover which the service is provided decreas-es; certain users who are located too farfrom the telephone company’s central of-fice may not be able to obtain the higherspeeds or, in some cases, may not be able toreceive the service at all.See also Asymmetric Digital SubscriberLine;High-Bit-RateDigitalSubscriberLine;Rate-Adaptive Digital Subscriber Line;Single-Line Digital Subscriber Line; Very-High-Bit-Rate Digital Subscriber versatile disc See digital video disc Abbreviated DVD;sometimes called digital versatile disc. Acompact disc format. A standard single-lay-er single-sided disc can currently store4.7GBofinformation;atwo-layerstandardincreases this to 8.5GB, and eventually dou-ble-sided discs are expected to store 17GBper disc. DVD drives can also read conven-tional compact video disc-erasable Abbreviat-ed DVD-E. An extension to the digital videodisc format to allow multiple re-recordings.See also digital video video disc-recordable Abbrevi-ated DVD-R. An extension to the digital vid-eo disc format to allow one-time recording.See also digital video video disc-ROM AbbreviatedDVD-ROM. A computer-readable form ofdigital video disc with either 4.7 or 8.5GBof storage per side.dimmed command In a graphical userinterface, a command that is not currentlyavailable. Also known as a grayed com-mand, because it is often displayed in lightgray rather than the usual black. For exam-ple, a command to perform a network ac-tion will be dimmed until you log on to thenetwork.DIN connector A connector that meetsthe specification of the German nationalstandards body, Deutsche Industrie Norm(DIN).SeveralmodelsofMacintoshcomputersuse8-pin DIN connectors as the serial port con-nector. On many IBM-compatible comput-ers, a 5-pin DIN connector connects thekeyboard to the system unit.DIP See dual in-line package.DIP switch A small switch used to selectthe operating mode of a device, mounted2461book Page 109 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 115. direct access110as a dual in-line package. DIP switches canbe either sliding or rocker switches, andthey are often grouped for convenience.They are used in printed circuit boards,dot-matrix printers, modems, and manyother peripheral devices.DIP SWITCHdirect access See random connection A communicationscircuit used for one specific purpose and notused by or shared with other users. Alsoknown as a dedicated circuit or a direct line.An ISDN qualifies as a direct connection.See also Integrated Services distance dialing AbbreviatedDDD. Use of the normal long-distance tele-phone system without the need for the in-tervention of an distance dial network See pub-lic line See direct manipulation In a graphical userinterface, the process of working with ob-jects using a mouse or other pointing device,rather than using menu selections to manip-ulate the objects. Using drag-and-drop toprint a file or using the mouse to adjust thesize of a window are both examples of memory access AbbreviatedDMA. A method of transferring informa-tion directly from a mass-storage device,such as a hard disk, into memory withoutthe information passing through the pro-cessor. Because the processor is not in-volved in the transfer, DMA is usually fast.2461book Page 110 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 116. 111Directory replicaDirectory 1. In Novell Directory Servic-es (NDS), the Directory database containsand organizes all the NDS objects.2. In the Microsoft Active Directory struc-ture, a Directory contains informationabout users, groups of users, computers,and so on.See also Active Directory; Directory ob-ject; Directory Schema; directory tree;Novell Directory In a hierarchical file system, aconvenient way of organizing and groupingfiles and other directories on a disk. Some-times called a folder. The beginning direc-tory is known as the root directory, fromwhich all other directories must branch.Directories inside another directory arecalled subdirectories.Depending on the operating system, youcan list the files in a directory in a variety ofways: by name, by creation date and time,by file size, or by icon if you use a graphicaluser interface.Seealsocurrentdirectory;defaultdirectory;directory services; file allocation table; par-ent directory; period and double-perioddirectories.Directory Access Protocol Abbreviat-ed DAP. A mail standard used to accesswhite page directories containing names,addresses, e-mail addresses, and telephonenumbers. Because of its complexity, DAPhas been largely replaced by LightweightDirectory Access Protocol (LDAP).See also Lightweight Directory caching A feature of NovellNetWare that copies the file allocationtable (FAT) and the directory entry tableinto the network server’s memory. Whenfile requests are made, information isretrieved from the cache rather than fromthe hard disk, thus speeding the retrievalprocess significantly. As the directory cachefills up, the least-used directory entries areeliminated from the hashing A feature of NovellNetWare that indexes file locations on disk,thus speeding file retrieval.Directory Map object In Novell Direc-tory Services (NDS), a leaf object that refersto a directory on a volume. The DirectoryMap object allows a drive to be mapped toan application or to a login script without re-quiring the actual path and volume wherethe application is physically located. This isdone so that login scripts don’t have to be re-written when a drive path changes; you cansimply change the Directory Map object.See also Novell Directory Services.Directory object In Novell DirectoryServices (NDS), a set of properties stored inthe Directory database. A Directory objectcan represent a physical or a logical net-work resource, but it does not actually con-tain the resource.See also Directory; Novell path See path.Directory replica In Novell NetWare, acopy of the NetWare Directory partition2461book Page 111 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 117. directory replication112that allows the NetWare Directory Data-base to be stored on several servers on thenetwork without having to duplicate theentire database on each server. Directoryreplicas remove a single point of failurefromthenetworkandtherebyincreasefaulttolerance.See also NetWare Directory replication A process thatcopies a master set of directories from aserver, called an export server, to otherspecified servers or workstations, known asimport computers. This process simplifiesthe task of maintaining and synchronizingidentical sets of directories and files, be-cause only one master copy of the data ismaintained. A file is replicated when it isadded to an exported directory, as well aswhen changes are made to the file.Directory Schema In Novell DirectoryServices (NDS), a set of rules that defineshow information can be stored in the Direc-tory database. The Schema contains fourmajor definitions:IAttribute information Describes thekinds of information that can be associat-ed with an object.IInheritance Defines which objects caninherit the rights and properties of otherobjects.INaming Determines the structure of theDirectory tree.ISubordination Specifies the location ofobjects in the Directory tree.See also Novell Directory service client AbbreviatedDSCLIENT. In Microsoft Windows 95/98,an add-on that makes a Windows 95/98 cli-ent computer aware of Active Directory.See also Active Directory.Directory Service log In MicrosoftWindows 2000 Server, a special log thatrecords any events associated with runningthe Directory Service, any problems con-necting to the global catalog, and anyevents associated with Active Directory(AD) on the network.See also DNS Server log; Event Viewer;File Replication Service log.Directory services In the Microsoft Ac-tive Directory structure, a directory as wellas the services it provides, such as securityand replication.See also Active services A listing of all usersandresourcesonanetwork,designedtohelpclients locate network users and services.Some examples are the OSI’s X.500, NovellDirectory Services (NDS), Microsoft’s Ac-tive Directory, and Banyan’s StreetTalk.See also domain directory services; globaldirectory structure duplication Atechnique that maintains duplicate copiesof the file allocation table (FAT) and direc-tory entry table in separate areas of a harddisk. If the first copy is damaged or de-stroyed, the second copy is immediatelyavailable for use.See also directory verification.2461book Page 112 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 118. 113disk cachedirectory tree A method of representingthe hierarchical structure of the directories,subdirectories, and files on a disk. The termis often used in graphical user interfaces. Inobject-oriented systems, this structure mayalso represent a group of objects, as in No-vell Directory Services (NDS).directory verification A process thatperforms a consistency check on duplicatesets of file allocation tables (FATs) and di-rectory entry tables to verify that they areidentical. The verification occurs every timethe server is started.See also directory structure duplication.disable To turn a function off or preventsomething from happening. In a graphicaluser interface, disabled menu commandsare often shown in gray to indicate that theyare not available.See also dimmed command; enable.disaster recovery The process used torestore services after a major interruption incomputing or in communications. Largeevents such as earthquakes or fires can inter-rupt networked computing activities, but socan more mundane events such as hard-diskfailureoraconstructionworkeraccidentallycutting through a power or telephone line.The whole point to disaster recovery is toplan for it before anything happens and thenfollow the plan when restoring services.See also backup; disk duplexing; disk mir-roring; redundant array of inexpensivedisks.Discretionary Access Control List Ab-breviated DACL. In Microsoft WindowsNT, a list of user and group accounts thathave permission to access an object’s ser-vices. The DACL has as many Access Con-trol Entries as there are user or groupaccounts with access to the object.disk cache Pronounced “disk cash.” Anarea of computer memory where data is tem-porarily stored on its way to or from a disk.When an application asks for informationfrom the hard disk, the cache program firstchecks to see if that data is already in thecache memory. If it is, the disk cache pro-gram loads the information from the cachememory rather than from the hard disk. Ifthe information is not in memory, the cacheprogram reads the data from the disk, cop-ies it into the cache memory for future ref-erence, and then passes the data to therequesting application. This process isshown in the accompanying illustration.Adiskcacheprogramcansignificantlyspeedmost disk operations. Some network operat-ing systems also cache other often accessedand important information, such as directo-ries and the file allocation table (FAT).See also directory caching.2461book Page 113 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 119. disk controller114DISK CACHEdisk controller The electronic circuitrythat controls and manages the operation offloppy disks and hard disks.A single disk controller may manage morethan one hard disk. Many disk controllersalso manage floppy disks and compatibletape drives. In the Macintosh, the disk con-troller is built into the system. In the PC, thedisk controller may be a printed circuitboard inserted into the expansion bus, or itmay be part of the hard disk drive itself.disk coprocessor board See host busadapter.disk drive A peripheral storage devicethat reads and writes magnetic or opticaldisks. When more than one disk drive is in-stalled on a computer, the operating systemassigns each drive (or logical drive) a uniquename.Several types of disk drives are in commonuse: floppy disk drives, hard disk drives,compactdiscdrives,digitalvideodiscdrives,Zip drives, and magneto-optical disc drives.disk duplexing A fault-tolerant tech-nique that writes the same information si-multaneously onto two hard disks.Each hard disk uses a different disk control-ler to provide greater redundancy. If onedisk or disk controller fails, informationfrom the other system can be used to con-tinue operations. Disk duplexing is offeredby most major network operating systems.It is designed to protect the system againsta single disk failure, not multiple disk fail-ures. Disk duplexing is no substitute for awell-planned series of disk backups.See also data protection; disk mirroring;redundant array of inexpensive disks.2461book Page 114 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 120. 115disk striping with parityDisk Manager In Microsoft Windows2000, the administrative tool used to man-age hard disks and other storage media.Disk Manager replaces NT’s Disk Admin-istrator.See also basic disk; dynamic disk.disk quotas In Microsoft Windows2000, a feature that allows an administra-tor to limit the amount of hard disk spaceavailable to a user. You can set quotas onlyon NTFS hard disks.diskless workstation A networkedcomputer that does not have any local diskstorage capability. The computer boots andloads all its programs from the network fileserver. Diskless workstations are particu-larly valuable when sensitive information isprocessed; information cannot be copiedfrom the file server onto a local disk, be-cause the workstation does not have one.See also dumb terminal; network com-puter; thin client.disk mirroring A fault-tolerant tech-nique that writes the same information si-multaneously onto two hard disks or twohard-disk partitions, using the same diskcontroller. If one disk or partition fails, in-formation from the other can be used tocontinue operations. Disk mirroring is of-fered by most major network operating sys-tems. It is designed to protect the systemagainst a single disk failure, not multiplediskfailures.Diskmirroringisnosubstitutefor a well-planned series of disk backups.See also data protection; disk duplexing;redundant array of inexpensive disks.disk optimizer A utility that rearrangesfiles and directories on a disk for optimumperformance. By reducing or eliminatingfile fragmentation (storage in pieces in dif-ferent locations on the hard disk), a diskoptimizer can restore the original level ofperformance of your disk system. Also, it isusually easier to undelete, or recover, anunfragmented file than a fragmented one.Many disk optimizers will not only rewritefiles as contiguous files, but will also placespecific unchanging files in particular loca-tions on the disk, optimize directories, andeven place specific applications on the diskso that they load more quickly.See also defragmentation.disk striping The technique of combin-ing a set of disk partitions located on differ-ent hard disks into a single volume, creatinga virtual “stripe” across the partitions thatthe operating system recognizes as a singledrive. Disk striping can occur at the bit levelor at the sector level and allows multipleconcurrent disk accesses that can improveperformance considerably.See also disk striping with parity; redun-dant array of inexpensive disks; stripe set.disk striping with parity The additionof parity information across a disk stripe sothat if a single disk partition fails, the dataon that disk can be re-created from the in-formation stored across the remaining par-titions in the disk stripe.See also disk striping; redundant array ofinexpensive disks; stripe set.2461book Page 115 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 121. dispersion116DISK STRIPINGdispersion The degree of scattering thattakes place as a beam of light travels alonga fiber-optic cable.See also cladding.distance vector algorithm A family ofrouting algorithms that calculate the best-path route to use for data transmissionfrom information present in adjacent nodeson the network. Routing information isbroadcast periodically rather than onlywhen a change occurs, which makes themethod bandwidth intensive. For this rea-son, distance vector algorithm is best usedin relatively small networks with few inter-router connections.Distinguished Name In Novell Directo-ry Services (NDS), the full name of an ob-ject, including the object’s Common nameand its context. Sometimes called the FullDistinguished Name.Seealso Commonname;Context;RelativeDistinguished Name.Distributed Component Object ModelAbbreviated DCOM. A specification fromMicrosoft that enables communications be-tween distributed objects.DCOM extends the Component ObjectModel (COM) so that clients can commu-nicate directly with other processes on dif-ferent computers on a LAN or on theInternet.See also ActiveX; Component ObjectModel.distributed computing See distributedprocessing.Distributed Computing EnvironmentAbbreviated DCE. The Open SoftwareFoundation’s (OSF) architecture for devel-oping application software for use on dif-ferent networks.2461book Page 116 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 122. 117DIX connectorDCEhidesthedifferencesbetweenproducts,technologies, and standards, providing inde-pendence from the operating system and un-derlying network. No particular communi-cations protocol is specified, so the networkcan run on IP (Internet Protocol), IPX (Inter-network Packet Exchange), or SNA (Sys-tems Network Architecture).distributed database A database man-aged as a single system even though it in-cludes many clients and many servers atboth local and remote sites. A distributeddatabase requires that data redundancy ismanaged and controlled.Distributed Director Web site load-bal-ancing software from Cisco Systems.A popular Web site can be overwhelmed byrequests from users, and to avoid long waittimes, you can configure additional Webservers to hold duplicate information. Webrequests are then sent to the Web server bestable to handle the request. Distributed Di-rector runs on Cisco routers and uses arouting protocol to send user requests to theserver that is closest to them.Distributed file system AbbreviatedDfs. In Microsoft Windows 2000 Server, ahierarchical file system that combines re-sources from all over the network into a sin-gle logical view.distributed file system Any file systemin which files and programs are located onmore than one computer or server. Userscan access files and applications as thoughthey were stored on a single local system.Distributed System Object ModelAbbreviated DSOM. IBM’s extension toSystem Object Model (SOM) that allowsobjects to communicate in a distributedprocessing environment.distributed processing A computersystem in which processing is performed byseveral separate computers linked by acommunications network.The term often refers to any computer sys-tem supported by a network, but moreproperly refers to a system in which eachcomputer is chosen to handle a specificworkload and the network supports thesystem as a whole. Each computer contrib-utes to the completion of a common task bycompleting one or more subtasks indepen-dently of its peers and then reporting the re-sults from these subtasks. All this is totallytransparent to the users; all they see are theresults of the process.See also client/server architecture.distribution groups In Microsoft Win-dows 2000 Server, a collection of recipiente-mail addresses. Distribution groups havenothing to do with system security. They donot have security identifiers, and they donot appear on access control lists.See also security groups.distribution medium The type of data-storage device used to distribute originalsoftware or software updates.Tapes used to be the favorite distributionmedium, but compact discs are rapidlygaining popularity.DIX connector See Attachment UnitInterface.2461book Page 117 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 123. DLL118DLL See Dynamic Link Library.DLSw See Data Link Switching.DMA See direct memory access.DMI See Desktop ManagementInterface.DNA See Digital Network Architecture.DNS See Domain Name Service.DNS alias A host name that the DomainNameService(DNS)serverknowspointstoanother host. Computers always have onereal name, but they can also have severalaliases. A DNS alias is sometimes called aCNAME or a canonical name.See also Domain Name Service.DNS name server A server containinginformation that is part of the DomainName Service (DNS) distributed database,which makes computer names available toclient programs querying for name resolu-tion on the Internet.See also Domain Name Service.DNS Server log In Microsoft Windows2000 Server, a special log that records anyevents associated with running the DomainName Service (DNS) Server.See also Directory Service log; Event View-er; File Replication Service log.docking station Ahardwaresystemintowhich a portable computer fits so that it canbe used as a full-fledged desktop computer.Docking stations vary from simple port rep-licators that allow you access to paralleland serial ports and a mouse to completesystems that give you access to networkconnections, CD-ROMs, and even a tapebackup system or PCMCIA ports. The por-table computer and docking station are de-signed as two parts of the same system; youcannot swap computers and docking sta-tions from different manufacturers or evenfrom different models.See also port replicator.document database A carefully orga-nized collection of related documents; forexample, a set of technical support bulletins.document instance In Standard Gener-alized Markup Language (SGML), the textcomponent of a document as distinct fromthe structure of the document.See also document type definition; Stan-dard Generalized Markup Language.document management The catalog-ing, storage, and retrieval of documents ina networked environment. In this context, adocument may be text, scanned graphics, aspreadsheet, a form, a Web page, or anyother unique file.Each file is tagged with information that in-cludes the name of the original author, doc-ument description, creation date, and thename of the application used to create thedocument.See also groupware; Lotus Notes; work-flow software.document root On a Web server, a di-rectory that contains the files, images, anddata you want to present to all users whoaccess the server with a browser.2461book Page 118 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 124. 119domain directory servicesdocument type definition Abbreviat-ed DTD. In Standard Generalized MarkupLanguage (SGML), the structural compo-nent of a document as distinct from the ac-tual data or content of the document.See also document instance; StandardGeneralized Markup Language.documentation The instructions, tuto-rials, specifications, troubleshooting ad-vice, and reference guides that accompany acomputer program or a piece of hardware.Documentation can be in printed or onlineformat. Early system documentation wasoften written by programmers and engi-neers and was usually filled with technicaljargon. Today’s documentation is generallybetter written and easier to understand.domain A description of a single com-puter, a whole department, or a completesite, used for naming and administrativepurposes.Top-level domains must be registered to re-ceive mail from outside the organization;local domains have meaning only insidetheir own enterprise. Depending on thecontext, the term can have several slightlydifferent meanings:IOn the Internet, a domain is part of theDomain Name Service (DNS).IIn Novell NetWare, a domain is a specialarea of memory where a new NetWareLoadable Module (NLM) can be testedwithout the risk of corrupting the operat-ing system memory.IIn IBM’s Systems Network Architecture(SNA),adomainrepresentsalltheterminalsandothernetworkresourcescontrolledbyasingle processor or processor group.IIn Microsoft Windows NT, a group ofcomputers, users, and network peripher-als managed with a single set of accountdescriptions and security policies. A usercan log on to the local computer and beauthenticated to access just that one sys-tem, or a user can log on to a domain andbe authenticated to access other serverswithin that domain.IIn Lotus Notes, a domain is one or moreNotes servers that share the same PublicName and Address Book database. Thisdatabase contains information about theusers within the domain, including their e-mail addresses and other information.See also domain name.domain component In the MicrosoftActive Directory structure, a portion of adomain name. For example, in, each element of the name—computer, sybex, and com—is a domaincomponent.See also Active Directory.domain controller In MicrosoftWindows NT, a server that stores andshares domain information, including thecentral database of users, passwords, andpermissions.A domain controller can be a primary do-main controller, which stores the mastercopy of the domain information, or a back-up domain controller, which uses a replicat-ed version of this data to verify user logonsand rights.domain directory services Directoryservices that consist of one or more linkedservers. Each domain within a network must2461book Page 119 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 125. domain name120be managed and administered separately.Windows NT Server and IBM’s LAN Serverboth use domain directory services.See also global directory services.domain name In the Domain Name Ser-vice (DNS), an easy-to-remember namethat identifies a specific Internet host, as op-posed to the hard-to-remember numeric IPaddress.See also bang path.Domain Name Service AbbreviatedDNS, sometimes referred to as DomainNaming System. A distributed addressingsystem that resolves the domain name intothe numeric IP address. DNS lets you usethe Internet without having to rememberlong lists of cryptic numbers.The most common high-level domains onthe Internet A commercial Aneducationalestablishmentsuchas a A branch of the U.S. An international A branch of the U.S. A network A nonprofit organizationMost countries also have unique domainsnamed after their international abbrevia-tion—for example, .uk for the United King-dom and .ca for Canada.See also IP address; name resolution.DOS Acronym for Disk Operating Sys-tem. An operating system originally devel-oped by Microsoft for the IBM PC.DOS existed in two similar versions:MS-DOS, developed and marketed byMicrosoft for use with IBM-compatiblecomputers, and PC-DOS, supported andsold by IBM for use on computers manu-factured by IBM.See also MS-DOS.DOS client A workstation that bootsMS-DOS and gains access to the networkusing either a NetWare shell or the Net-Ware DOS Requester software.DOS prompt See MS-DOS A synonym for the name of the cur-rent directory, usually invisible as its namebegins with a period.In Unix, a file whose name begins with a dotusually contains configuration informa-tion; you can customize your environmentby creating the appropriate dot file in thecurrent directory or in your home directory.See also current directory; dot dot; periodand double-period dot A synonym for the name of theparent directory to the current directory,usually invisible as its name begins with aperiod.See also current directory; dot; period anddouble-period directories.dotted decimal A method of represent-ing an IP address as four decimal numbers2461book Page 120 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 126. 121drag-and-dropseparated by dots, or periods; for example, also IP address.double-byte character set Abbreviat-ed DBCS. A method that uses two bytes tohold the definition of the character ratherthan the single byte used by the AmericanStandard Code for Information Interchange(ASCII) or the Extended Binary Coded Dec-imal Interchange Code (EBCDIC).By utilizing two bytes instead one, the manyinternational character sets in use thesedays can be managed much more easily.See also ASCII standard character set;ASCII extended character set; Unicode.double-slash Notation used with a co-lon to separate the communications proto-col from the host computer name in aUniform Resource Locator (URL) as in also Uniform Resource Locator.downlevel trust In Microsoft Windows2000 Server, a trust explicitly establishedbetween a Windows 2000 domain and aWindows NT 4 domain.See also explicit trust; shortcut trust; trustrelationship; two-way transitive trust.downlink The transmission of informa-tion from a satellite to an earth station.See also 1. In communications, totransfer a file or files from one computer toanother over a network or using a modem.2. To send information, such as font infor-mation or a PostScript file, from a computerto a printer.downsizing The redesign of mainframe-based business applications to applica-tions capable of running on smaller, less-expensive systems, often PC LANs. Client/server architecture is the model most oftenimplemented during downsizing.When applications are moved from largecomputer systems to PCs, security, integri-ty, and overall control may be compro-mised, and development and training costscan be high. However, a collection of ap-propriately configured PCs, networked to-gether, can provide more than ten times thepower for the same cost as a mainframecomputer supporting remote terminals.A more accurate term might be rightsizing,to match the application requirements ofthe corporation to the capabilities of thehardware and software systems available.See also outsourcing.downtime The amount of time duringwhich a computer system is not available tousers, because of a hardware or softwarefailure.downward compatibility See back-ward compatibility.DP See data processing.drag-and-drop In a graphical user inter-face, to move a selected object onto anotherobject with the mouse to initiate a process.For example, if you drag a document iconand drop it onto a word processor’s icon,the program will run, and the document2461book Page 121 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 127. DRAM122will be opened. To print a file, you can dragthe file to the printer icon using the mouseand then release the mouse button. You canalso use drag-and-drop to copy a file fromone disk to another or to move a markedblock of text to a new location inside aword-processed document.DRAM See dynamic array The group of hard diskdrives used in one of the RAID (redundantarray of inexpensive disks) configurations.See also redundant array of letter Adesignationusedtospecifya PC disk drive. For example, the first flop-py disk drive is usually referred to as driveA, and the first hard disk drive is usually re-ferred to as drive mapping The technique of assign-ing a drive letter to represent a completedirectory path statement. Novell NetWaresupports four types of drive mapping:ILocal drive mapping Maps drives to lo-cal hard disk and floppy disk drivesINetwork drive mapping Maps drives tovolumes and directories on the networkINetwork search drive mapping Mapsdrives to directories that should besearched if an application or file is notfound in the current directoryIDirectory map object Maps drives to di-rectories that contain frequently usedfiles, such as applications, without havingto specify the actual physical location ofthe fileSee also Directory Map object.driver Jargon for device driver.See also device driver.drop 1. The location in a multidrop linewhere a tap is inserted to allow the connec-tion of a new device.2. To lose part of a signal, usually uninten-tionally, as in dropping bits.drop cable The cable used in thick Ether-net to connect a network device to a Multi-station Access Unit (MAU). The maximumcable length is 50 meters (165 feet). Some-times called a transceiver cable.DS See digital signal.DSCLIENT See directory service client.DSL See Digital Subscriber Line.DSOM See Distributed System ObjectModel.DSP See Digital Signal Processing.DSR See Data Set Ready.DSU See Data Service Unit.DTD See document type definition.DTE See data terminal equipment.DTR See Data Terminal Ready; Dedicat-ed Token Ring.dual-attached station AbbreviatedDAS. In the Fiber Distributed Data Inter-face (FDDI), a device attached to both ofthe dual, counter-rotating rings. Concen-trators, bridges, and routers often use DASconnections to provide fault tolerance. Incontrast, a single attached station (SAS)connects to only one ring.2461book Page 122 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 128. 123Dynamic Data Exchangedual-homed host A network serverconfigured with two network interfacecards, each connected to a different net-work. Dual-homed hosts are often usedwith firewalls to increase network security.See also firewall; proxy server.dual homing In Fiber Distributed DataInterface (FDDI), a method of cabling con-centrators and stations in a tree configura-tion, providing an alternative route to theFDDI network should the primary connec-tion fail.dual in-line package Abbreviated DIP.A standard housing constructed of hardplastic commonly used to hold an integrat-ed circuit. The circuit’s leads are connectedto two parallel rows of pins designed to fitsnugly into a socket; these pins may also besoldered directly to a printed circuit board.See also DIP switch.dumb terminal A combination of key-board and screen that has no local comput-ing power, used to input information to alarge, remote computer, often a minicom-puter or a mainframe. The remote comput-er provides all the processing power for thesystem.See also diskless workstation; intelligentterminal; network computer; thin client.duplex In asynchronous transmissions,the ability to transmit and receive on thesame channel at the same time; also referredto as full duplex. Half-duplex channels cantransmit only or receive only.See also communications parameters.DVD See digital video disc.DVD-E See digital video disc-erasable.DVD-R See digital video disc-recordable.DVD-ROM See digital video disc-ROM.dynamic adaptive routing See dy-namic routing.dynamic bandwidth allocation Amethod of bandwidth allocation that sub-divides the available bandwidth betweenmultiple applications almost instanta-neously, to provide each application withjust the amount of bandwidth that it cur-rently needs.Dynamic Data Exchange AbbreviatedDDE. A technique used for application-to-application communications, available inseveral operating systems, including Mi-crosoft Windows, Macintosh, and OS/2.When two or more programs that supportDDE are running at the same time, they canexchange data and commands, by means ofconversations. A DDE conversation is atwo-way connection between two applica-tions, used to transmit data by each pro-gram alternately.DDE is used for low-level communicationsthat do not need user intervention. For ex-ample, a communications program mightfeed stock market information into aspreadsheet program, where that data canbe displayed in a meaningful way and recal-culated automatically as it changes.DDE has largely been superseded by ObjectLinking and Embedding (OLE).See also Object Linking and Embedding.2461book Page 123 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 129. dynamic disk124dynamic disk In Microsoft Windows2000, a hard disk that is available only toWindows 2000 and not available from anyother operating system. A dynamic diskdoes not use primary and extended parti-tions to divide the available space into log-ical units.To create a dynamic disk, use the DiskManagement utility to convert a basic diskinto a dynamic disk. Dynamic disks allowyou to create, delete, and extend fault-tol-erant and multidisk volumes without re-starting the operating system. Windows2000 RAID (redundant array of inexpen-sive disks) services are available only on dy-namic disks.See also basic disk.Dynamic DNS Abbreviated DDNS. InMicrosoft Windows 2000 Server, a mecha-nism that allows Dynamic Host Configura-tion Protocol (DHCP) and Windows 2000clients to update Domain Name Service(DNS) records dynamically, rather than bythe traditional method of manually addingthe new records to static DNS zone files.See also Domain Name Service.Dynamic Host Configuration ProtocolAbbreviated DHCP. A system based on net-work interface card addresses that is used toallocate IP addresses and other configura-tion information automatically for net-worked systems. DHCP is an update of theBootstrap Protocol.See also Bootstrap Protocol; hardware ad-dress; IP address; Transmission ControlProtocol/Internet Protocol.Dynamic Link Library AbbreviatedDLL. A program module that contains ex-ecutable code and data that can be used byapplications, or even by other DLLs, in per-forming a specific task.DLLs are used extensively throughout thefamily of Microsoft Windows products.DLLs may have filename extensions of.DLL, .DRV, or .FON.The DLL is linked into the application onlywhen the program runs, and it is unloadedagain when no longer needed. If two DLLapplications are running at the same timeand both perform a particular function, onlyone copy of the code for that function isloaded, for more efficient use of limitedmemory. Another benefit of using dynamiclinking is that the .EXE files are not as largeas they would be, because frequently usedroutines can be put into a DLL rather thanrepeated in each .EXE file that uses them. Asmaller.EXEfilemeanssaveddiskspaceandfaster program loading.dynamic RAM Abbreviated DRAM,pronounced “dee-ram.” A common type ofcomputer memory that uses capacitors andtransistors storing electrical charges to rep-resent memory states. These capacitors losetheir electrical charge, so they need to be re-freshed every millisecond, during whichtime they cannot be read by the processor.DRAM chips are small, simple, cheap, easyto make, and hold approximately fourtimes as much information as a static RAM(SRAM) chip of similar complexity. How-ever, they are slower than SRAM.dynamic routing A routing techniquethat allows the route that a message takes to2461book Page 124 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 130. 125DynaTextchange, as the message is in transit throughthe network, in response to changing net-work conditions. Conditions forcing a routechangemightincludeunusuallyheavytrafficon a particular section of the network or acable failure. Also known as dynamic adap-tive routing.dynamic volume In Microsoft Win-dows 2000, a logical hard disk volume cre-ated by Disk Management.Dynamic volumes can include simple,striped, spanned, and RAID-5 componentsand can exist only on dynamic disks.See also basic disk; dynamic disk.DynaText A form of electronic docu-ment and viewer used in Novell NetWarefor online manuals. You can use DynaTextdirectly from the CD, or you can install it onthe server or on a workstation. ReplacesElectrotext.2461book Page 125 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 131. E126EE See exa-.E1 A point-to-point, dedicated,2.048Mbps communications circuit capa-ble of supporting thirty-two 64Kbps chan-nels used as 30 voice channels, 1 controlchannel, and 1 synchronization and fram-ing channel. The European equivalent ofNorth America’s T1.E1 circuits carry more channels than the 24channels used in T1 systems, and repeatersare required every 6000 feet when copperwire is used.E2 A European point-to-point, dedicat-ed, 8.848Mbps communications circuitequivalent to four E1 circuits. E2 is the Eu-ropean equivalent of North America’s T2and is rarely used.E3 AEuropeanpoint-to-point,dedicated,34.368Mbps communications circuitequivalent to 16 E1 circuits. The Europeanequivalent of North America’s T3.E4 AEuropeanpoint-to-point,dedicated,139.26Mbps communications circuitequivalent to 4 E3 or 64 E1 circuits.E5 AEuropeanpoint-to-point,dedicated,565.148Mbps communications circuitequivalent to 4 E4 or 256 E1 circuits.EAP See Extensible AuthenticationProtocol.eavesdropping Theprocessofgatheringinformation about a target network by lis-tening in on transmitted data.EB See exabyte.EBCDIC See Extended Binary CodedDecimal Interchange Code.echo 1. A transmitted signal that is re-flectedbacktothesenderstronglyenoughsothat it can be distinguished from the originalsignal; often encountered on long-distancetelephone lines and satellite links.2. A form of repetition, used as a mecha-nism in testing network nodes, in whicheach receiving station on the network ech-oes a message back to the main server orhost computer.echo cancellation A mechanism used tocontrol echoes on communications linkssuch as satellite links.The modem checks for a delayed duplica-tion of the original signal and adds a re-versed version of this transmission to thechannel on which it receives information.This process effectively removes the echowithout affecting the incoming signal.ECNE See Master Certified NovellEngineer.EDI See electronic data interchange.EDO RAM Abbreviation for extendeddata out RAM. A type of RAM that keepsdata available to the processor while thenext memory access is being initialized,thus speeding overall access times. EDORAM is significantly faster than conven-tional dynamic RAM.2461book Page 126 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 132. 127electromagnetic interferenceEDP See data processing.EEMS See Enhanced Expanded Mem-ory Specification.effective rights In Novell Directory Ser-vices (NDS), any rights an object can use tolook at or change a specific directory, file,or other object.Effective rights are recalculated every timean object attempts such an operation andarecontrolledbytheInheritedRightsFilter,the trustee assignment, and the specified se-curity restrictions. Effective rights are oftwo types:IObject rights determine what a user cando with an object.IProperty rights control a user’s access tothat object.See also Inherited Rights Filter; NovellDirectory Services; rights; trusteeassignments.EFS See Encrypted File System.EGP See External Gateway Protocol.EIA See Electronic IndustriesAssociation.EIA/TIA 586 A standard, jointly definedby the Electronic Industries Associationand the Telecommunications Industry As-sociation (EIA/TIA), for telecommunica-tions wiring used in commercial buildings.The standard is designed to do thefollowing:ISpecify a generic wiring system for allcommercial buildingsIDefine media types, as well as connectionsand terminationsIProvide a basis for interoperationbetween competing products and servicesin wiring, design, installation, andmanagementIAllow for the wiring of a building beforethe definition of the products that will usethat wiring, and allow for elegant futureexpansionEIA/TIA 586 applies to all unshieldedtwisted-pair wiring that works with Ether-net, Token Ring, ISDN, and other net-working systems.See also cabling standards; Category 1–5.EIDE See Enhanced IDE.EIGRP See Enhanced Interior GatewayRouting Protocol.EISA See Extended Industry StandardArchitecture.electromagnetic interference Abbre-viated EMI. Any electromagnetic radiationreleased by an electronic device that dis-rupts the operation or performance of an-other device.EMI is produced by many sources com-monly found in an office environment, in-cluding fluorescent lights, photocopiers,and motors such as those used in elevators.EMI is also produced by natural atmo-spheric or solar activity.See also Class A certification; Class B cer-tification; Federal Communications Com-mission; radio frequency interference.2461book Page 127 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 133. electronic commerce128electronic commerce The buying andselling of goods and services over the Inter-net. Electronic commerce may also involvebusiness-to-business transactions in the ex-change of purchase orders, invoices, andother electronic documents.electronic data interchange Abbrevi-ated EDI. A method of electronically ex-changing business documents, includingbills of materials, purchase orders, andinvoices.Customers and suppliers can establish anEDI network by means of Open Systems In-terconnect (OSI) standards or by using pro-prietary products. Widely acceptedstandards include ANSI X.12, ISO 9735,and CCITT X.435.electronic data processing See dataprocessing.Electronic Industries Association Ab-breviated EIA. A trade association repre-senting American manufacturers instandards organizations. The EIA haspublishedandformalizedseveralimportantstandards, including RS-232-C, RS-422,RS-423, RS-449, RS-485, and RS-530.Standards having to do with communica-tions are produced jointly with the Tele-communications Industry Association.For more information on the EIA, also EIA/TIA 586.electronic mail The use of a network totransmit text messages, memos, and re-ports; usually referred to as e-mail. Userscan send a message to one or more individ-uals, to a predefined group, or to all userson the system. When you receive a message,you can read, print, forward, answer, or de-lete it.An e-mail system may be implemented on apeer-to-peer network, a client/server archi-tecture, a mainframe computer, or on adial-up service, such as America Online. E-mail is by far the most popular Internet ap-plication, with well over 80 percent of In-ternet users taking advantage of the service.E-mail has several advantages over conven-tional mail systems, including:IE-mail is fast—very fast when comparedwith conventional mail.IIf something exists on your computer as afile—text, graphical images, even pro-gram files and video segments—you canusually send it as e-mail.IE-mail is very extensive. You can nowsend e-mail to well over half the countriesin the world.The problems associated with e-mail aresimilar to those associated with online com-munications in general, such as security,privacy (always assume that your e-mail isnot private), and the legal status of docu-ments exchanged via e-mail.See also mailbox; Multipurpose InternetMail Extension; voice mail.element A unit of structure in Hyper-Text Markup Language (HTML), such as atitle or a list. Some elements have start andstop tags; others have only a single tag. Cer-tain elements can be nested within otherelements.See also HyperText Markup Language; tag.2461book Page 128 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 134. 129enableelevator seeking A technique that al-lows the server hard disk head to access filesin the direction that the head is already trav-eling across the disk, rather than in the or-der in which they were requested. Thisfeature allows the drive heads to operatecontinuously and thus improves disk per-formance and minimizes disk-head seektimes.ELF See extremely low-frequencyemission.EMA See Enterprise MemoryArchitecture.emacs A popular Unix editor, written byRichard Stallman, founder of the Free Soft-ware Foundation.The nameemacs is a contraction of “editingmacros,” but it is much more than a simpletext editor and includes extensions for allsorts of common tasks, ranging from com-piling and debugging programs to readingand sending e-mail. You can even extendemacs yourself as the editing commands arewritten in the Lisp programming language.See also Free Software Foundation; vi.e-mail See electronic mail.e-mail address The addressing informa-tion required for an e-mail message to reachthe correct recipient.See also bang path; Internet address;mailbox.Emergency Repair Disk AbbreviatedERD. In Microsoft Windows 2000, a flop-py disk created by the Backup program. AnERD contains information about the cur-rent system configuration that can be usedto repair a system that will not restart.See also Recovery Console; safe mode.EMI See electromagnetic interference.EMM See expanded memory manager.emoticon A collection of text charactersoften used in e-mail and posts to news-groups to signify emotions.An emoticon can be as simple as including<g> or <grin> in your text, an indicationthat the writer is joking, and as complex assome of the smiley faces, which are all de-signed to be read sideways, such as the wink;-) or the frown :-(.See also Internet abbreviations.EMS See Expanded MemorySpecification.emulator A device built to work exactlylike another device—hardware, software,or a combination of both.For example, a terminal emulation pro-gram lets a PC pretend to be a terminal at-tached to a mainframe computer or to anonline service by providing the controlcodes that the remote system expects to re-ceive. In printers, some brands emulatepopular models such as Hewlett-Packard’sLaserJet line.enable To turn a function on or allowsomething to happen. When a function isenabled, it is available for use. In a graphi-cal user interface, enabled menu commandsare often shown in black type.See also disable.2461book Page 129 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 135. Encapsulated PostScript130Encapsulated PostScript AbbreviatedEPS. The file format of the PostScript page-description language.The EPS standard is device independent, soimages can easily be transferred betweenapplications, and they can be sized and out-put to different printers without any loss ofimage quality or distortion.The EPS file contains the PostScript com-mands needed to recreate the image, butthe image itself cannot be displayed on amonitor unless the file also contains an op-tional preview image stored in TIFF orPICT format.You can print an EPS file only on a Post-Script-compatible laser printer, and theprinter itself determines the final printingresolution. A laser printer might be capableof 600 dpi, whereas a Linotronic printer iscapable of 2450 dpi.encapsulation The process of insertingthe frame header and data from a higher-level protocol into the data frame of alower-level protocol.See also tunneling.enclosure A term for a file—text, fax, bi-nary, or image—sent as a part of an e-mailmessage. Sometimes called an attachment.See also Multipurpose Internet MailExtension.encode 1. To compress a video file usinga codec so that the file can be transmitted inthe shortest possible time.2. To convert a binary file into a form suit-able for data transmission.See also codec; decode; decryption;uuencode.Encrypted File System In MicrosoftWindows 2000, a feature that lets mobileusers, who are concerned with the securityof their files in the case of unauthorizedaccess to their computers, encrypt designat-ed files and directories using a public keyencryption scheme.Encrypting File System AbbreviatedEFS. In Microsoft Windows 2000, a file sys-tem used to encrypt files and folders on anNTFS 5 hard disk.encryption The process of encoding in-formation in an attempt to make it securefrom unauthorized access, particularly dur-ingtransmission.Thereverseofthisprocessis known as decryption.Two main encryption schemes are in com-mon use:IPrivate (Symmetrical) Key An encryp-tion algorithm based on a private encryp-tion key known to both the sender and therecipient of the information. The encrypt-ed message is unreadable and can betransmitted over nonsecure systems.IPublic (Asymmetrical) Key An encryp-tion scheme based on using the two halvesof a long bit sequence as encryption keys.Either half of the bit sequence can be usedto encrypt the data, but the other half is re-quired to decrypt the data.See also Data Encryption Standard; PrettyGood Privacy; ROT-13.2461book Page 130 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 136. 131Enhanced Interior Gateway Routing Protocolencryption key A unique and secretnumber used to encrypt data to protect itfrom unauthorized access.end-of-file Abbreviated EOF. A specialcode placed after the last byte in a file thatindicates to the operating system that nomore data follows.An end-of-file code is needed because diskspace is assigned to a file in blocks, and thefile may not always terminate at the end ofa block. In the ASCII system, an EOF is rep-resented by the decimal value 26 or by theCtrl+Z control character.end node A networked node such as aPC that can only send and receive informa-tion for its own use; it cannot route or for-ward information to another node.end-of-text Abbreviated ETX. A charac-ter used in computer communications to in-dicate the end of a text file.In the ASCII system, an ETX is representedby the decimal value 3 or by the Ctrl+C con-trol character. A different symbol, end-of-transmission (EOT, ASCII 4, or Ctrl+D)is used to indicate the end of a completetransmission.end-of-transmission AbbreviatedEOT. A character used in computer com-munications to indicate the end of a trans-mission. In the ASCII system, an EOT isrepresented by the decimal value 4 or by theCtrl+D control character.end user Often refers to people who usean application to produce their own resultson their own computer or workstation.During the mainframe computer era, endusers were people who received outputfrom the computer and used that output intheir work. They rarely, if ever, actuallysaw the computer, much less learned to useit themselves. Today, end users often writemacros to automate complex or repetitivetasksandsometimeswriteproceduresusingcommand languages.Enhanced Expanded MemorySpecification Abbreviated EEMS. A re-vised version of the original Lotus-Intel-MicrosoftExpandedMemorySpecification(LIM EMS) that lets MS-DOS applicationsuse more than 640KB memory space.See also Expanded Memory Specification.Enhanced IDE An extension to the Inte-grated Drive Electronics (IDE) interfacestandard, which supports hard disks aslarge as 8.4GB (IDE supports hard disks ofup to 528MB) and transfer rates of up to13.3MBps (IDE allows rates of up to3.3MBps).See also Integrated Drive Electronics;Small Computer System Interface.Enhanced Interior Gateway RoutingProtocol Abbreviated EIGRP. A propri-etary link-state distance-vector routing pro-tocol from Cisco, first released in 1994.EIGRP improves performance by using in-formation derived from distance-vectorprotocols, but also includes an algorithmfor removing transient loops in possibleroutes, which reduces the complexity of thecalculations required.Seealsodistancevectoralgorithm;InteriorGateway Routing Protocol.2461book Page 131 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 137. Enhanced Small Device Interface132Enhanced Small Device Interface Ab-breviated ESDI. A popular hard disk, flop-py disk, and tape drive interface standard,capable of a data-transfer rate of 10 to20Mbps. ESDI is most often used with largehard disks.See also Integrated Drive Electronics;Small Computer System Interface.ENS See Enterprise Network Services.Enter key Also known as the Return key,short for carriage return. The key that indi-cates the end of a command or the end ofuser input from the keyboard.enterprise A term used to encompass anentire business group, organization, or cor-poration, including all local, remote, andsatellite offices.Enterprise CNE See Master CertifiedNovell Engineer.Enterprise Memory Architecture Ab-breviated EMA. In Microsoft Windows2000, a mechanism that lets applications ad-dress as much as 64GB of virtual memory.enterprise network A network thatconnects every computer in every locationof a business group, organization, or cor-poration and runs the company’s mission-critical applications.In many cases, an enterprise network in-cludes several types of computers runningseveral different operating systems.Enterprise Network Services Abbre-viated ENS. A software product based onBanyan Systems’ StreetTalk Directory Ser-vice for VINES that brings global directoryservice features to other networks. ENS in-cludes StreetTalk Directory Assistance, theBanyan Security Service, and Banyan Net-work Management.Specific versions of ENS are available forNovellNetWare,SCOUnix,andHP-UXsothat servers running those operating sys-tems can interoperate and share manage-ment in a network with VINES servers.See also Banyan VINES.Enterprise Systems Connection Ab-breviated ESCON. A set of products and ser-vices from IBM that provide direct channel-to-channel connections between ES/9000mainframes and peripheral devices over 10to 17MBps fiber-optic links.envelope delay See delay distortion.environment 1. The complete set ofhardware and software resources madeavailable to any user of a system.2. The operating system that a programneeds in order to execute. For example, aprogram may be said to be running in theUnix environment.EOF See end-of-file.EOT See end-of-transmission.EPS See Encapsulated PostScript.equalization The process of balancing acircuit by reducing frequency and phasedistortion so that it passes all expected fre-quencies with equal efficiency.ERD See Emergency Repair Disk.error The difference between the expect-ed and the actual.2461book Page 132 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 138. 133escape sequenceIn computing, the way that the operatingsystem reports unexpected, unusual, im-possible, or illegal events is by displaying anerror number or error message. Errorsrange from trivial, such as an attempt towrite a file to a disk drive that does not con-tain a disk, to fatal, such as when a seriousoperating system bug renders the systemuseless.In communications, errors are often causedby line noise and signal distortion. Parity orcyclical redundancy check (CRC) informa-tion is often added as overhead to the datastream, and techniques such as error detec-tion and correction are employed to detectand correct as many errors as possible.See also attenuation; crosstalk; errorhandling; error message; error rate;parity error.error detection and correction Amechanism used to determine whethertransmission errors have occurred and, ifso, to correct those errors.Some programs or transmission protocolssimply request a retransmission of the af-fected block of data if an error is detected.More complex protocols attempt to bothdetect and determine at the receiving endwhat the correct transmission should havebeen.See also checksum; cyclical redundancycheck; forward error correction; Hammingcode; parity.error handling The way that a programcopes with errors or exceptions that occuras the program is running.Good error handling manages unexpectedevents or wrongly entered data gracefully,usually by opening a dialog box to promptthe user to take the appropriate action or toenterthecorrectinformation.Badlywrittenprograms may simply stop running whenthe wrong data is entered or when an unan-ticipated disk error occurs.error message A message from the pro-gram or the operating system that containsinformation about a condition that requiressome human intervention to solve.Error messages can indicate relatively triv-ial problems, such as a disk drive that doesnot contain a disk, as well as fatal problems,such as when a serious operating systembug renders the system useless and requiresa system reboot.error rate In communications, the ratiobetween the number of bits received incor-rectly and the total number of bits in thetransmission, also known as bit error rate(BER).Somemethodsfordeterminingerrorrateuselarger or logical units, such as blocks, pack-ets, or frames. In these cases, the measure-mentoferrorrateisexpressedintermsofthenumber of units found to be in error out ofthe total number of units transmitted.escape code See escape sequence.Escape key The key on the keyboard la-beled Esc. The Escape key generates an es-cape code, ASCII 27. In most applications,pressing the Escape key cancels the currentcommand or operation.escape sequence A sequence of charac-ters, beginning with Escape (ASCII 27) and2461book Page 133 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 139. ESCON134followed by one or more other characters,that performs a specific function. Some-times called an escape code.Escape sequences are often used to controlprinters or monitors, which treat them ascommands and act upon them rather thanprocessing them as characters to print ordisplay.ESCON See Enterprise SystemsConnection.ESDI See Enhanced Small DeviceInterface.Ethernet A popular network protocoland cabling scheme with a transfer rate of10Mbps, originally developed at Xerox in1970 by Dr. Robert Metcalf. Ethernet usesa bus topology, and network nodes are con-nected by either thick or thin coaxial cable,fiber-optic cable, or twisted-pair cable.Ethernet uses CSMA/CD (Carrier SenseMultiple Access/Collision Detection) toprevent network failures or collisions whentwo devices try to access the network at ex-actly the same time.The original DIX (Digital Equipment,Intel, Xerox), or Blue Book, standard hasevolved into the slightly more complexIEEE 802.3 standard and the ISO’s 8802.3specification.The advantages of Ethernet include:IIt’s easy to install at a moderate cost.ITechnology is available from many sourc-es and is very well known.IIt offers a variety of cabling options.IIt works very well in networks with onlyoccasional heavy traffic.And the disadvantages include:IHeavy traffic can slow down the network.IA break in the main cable can bring downlarge parts of the network.ITroubleshooting a bus topology canprove difficult.Seealso 10/100;100VG-AnyLAN;10Base2;10Base5; 10BaseF; 10BaseT; demand pri-ority; Fast Ethernet; Gigabit Ethernet.Ethernet address The address assignedto a network interface card by the originalmanufacturer or by the network adminis-trator if the card is configurable.This address identifies the local device ad-dress to the rest of the network and allowsmessages to reach the correct destination.Also known as the media access control(MAC) or hardware address.Ethernet meltdown An event that caus-es saturation on an Ethernet-based system,often the result of illegal or misdirectedpackets. An Ethernet meltdown usuallylasts for only a short period of time.Ethernet packet A variable-length unitin which information is transmitted on anEthernet network.An Ethernet packet consists of a synchroni-zation preamble, a destination address, asource address, a field that contains a typecode indicator, a data field that can varyfrom 46 to 1500 bytes, and a cyclical redun-dancy check (CRC) that provides a statisti-cally derived value used to confirm theaccuracy of the data.2461book Page 134 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 140. 135executeETHERNET PACKETEtherTalk An implementation of theEthernet LAN developed for Apple com-puters, designed to work with the Apple-Share network operating system.EtherTalkoperatesovercoaxialcableattheEthernet transfer rate of 10Mbps, muchfaster than the 230.4Kbps rate availablewith AppleTalk. Each networked Macin-tosh computer must be supplied with a spe-cial EtherTalk network interface card.ETX See end-of-text.Eudora A popular and widely usede-mail application originally developed bySteve Dorner at the University of Illinoisand now available from Qualcomm, Inc.European Laboratory for ParticlePhysics See Conseil Européen pour laResearche Nucléaire.even parity See parity.Event Log service A Microsoft Win-dows 2000 service that logs important ap-plication, security, and system events intothe event log.Event Viewer In Microsoft Windows2000, a utility that displays the contents ofthe system logs.See also application log; Directory Servicelog; DNS Server log; File Replication Ser-vice log; security log; system log.exa- Abbreviated E. A prefix meaning onequintillion, or 1018. In computing, the prefixmeans 1,152,921,504,606,846,976, or thepower of 2 closest to one quintillion (260).exabyte Abbreviated EB. 1 quintillionbytes, or 1,152,921,504,606,846,976bytes.exclusive container administrator InNovell NetWare, a special type of containeradministrator who is given the rights to acontainer and all the objects within thatcontainer. The Inherited Rights Filter pre-vents other administrators from havingrights in the container.Seealsocontaineradministrator;InheritedRights Filter.executable file Any file that can be exe-cuted by the operating system. Some exe-cutable files contain compiler binaryinstructions, and others are text files con-taining commands or shell scripts.execute 1. To run a program, com-mand, or script.2461book Page 135 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 141. execute permission1362. One of the permissions assigned to a fileor directory; you can only execute a filewhen the execute permission is enabled.execute permission An access permis-sion on a file or directory that gives you per-mission to execute the file or to access thecontents of the directory.expandability The ability of a system toaccommodate expansion. In hardware, thismay include the addition of more memory,more or larger disk drives, and new adapt-ers. In software, expandability may includethe ability of a network to add users, nodes,or connections to other networks.expanded memory An MS-DOS mech-anism by which applications can accessmore than the 640KB of memory normallyavailable to them. The architecture of theearly Intel processors restricted the originalIBM PC to accessing 1MB of memory,640KB of which was available for applica-tions; the remaining 384KB was reservedfor system use, the BIOS, and the video sys-tem. At that time, 640KB was more than tentimes the amount of memory available inother personal computers. However, asboth applications and MS-DOS grew, theybegan to run out of room.The Expanded Memory Specification LIM4.0 let programs running on the Intel familyof processors access as much as 32MB of ex-panded memory. The expanded memorymanager (EMM) creates a block of addressesinto which data (held in memory above the1MB limit) is swapped in and out as neededby the program. In other words, a 64KB seg-ment of addressable memory creates a smallwindow through which segments of expand-edmemorycanbeseen,butonlyonesegmentat a time.expanded memory manager Abbrevi-ated EMM. A device driver that supportsthe software portion of the ExpandedMemory Specification (EMS) in an IBM-compatible computer.Expanded Memory Specification Ab-breviated EMS. The original version of theLotus-Intel-Microsoft Expanded MemorySpecification (LIM EMS), which let MS-DOS applications use more than 640KB ofmemory space.These days Microsoft Windows running inprotected mode on 80386 and later proces-sors is free of this limitation.expansion board A printed circuitboard that plugs into a computer’s expan-sion bus to provide added capabilities. Alsocalled an adapter.Common expansion boards include videoadapters, joy-stick controllers, and input/output (I/O) adapters, as well as other de-vices, such as internal modems, CD-ROMs,and network interface cards (NICs). Oneexpansion board can often support severaldifferent devices. Some current PC designsincorporate many of the functions previ-ously performed by these individual adapt-ers on the motherboard.expansion bus Anextensionofthemaincomputer bus that includes expansion slotsfor use by compatible adapters, such asmemory boards, video adapters, hard-disk2461book Page 136 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 142. 137Extended Industry Standard Architecturecontrollers, and SCSI (Small Computer Sys-tem Interface) interface cards.expansion slot One of the connectorson the expansion bus that gives an adapteraccess to the system bus. You can install asmany additional adapters as there are ex-pansion slots inside your computer.For portable computers, an expansion slotis often supplied by a PCMCIA connectiondesigned to accept a PC Card.expansion unit An external housingavailable with certain portable computersdesigned to contain additional expansionslots and maintain a connection to the mainexpansion bus in the computer’s system unit.See also port replicator.explicit rights In Novell Directory Ser-vices (NDS), any rights granted directly to auser for a directory or other NDS object.Explicit rights always override inheritedrights.See also inherited rights.explicit security equivalence In Nov-ell Directory Services (NDS), a techniqueused to give one trustee the same rights asanother trustee. Explicit security equiva-lence can be assigned with group member-ship, an Organizational Role, or thetrustee’s Security Equal To property.See also implied security equivalence;security equivalence.explicit trust In Microsoft Windows2000 Server, a trust explicitly establishedbetween two Windows 2000 domains. Thisis in addition to the built-in transitive trustsautomatically established if they are in thesame forestSee also downlevel trust; forest; shortcuttrust; trust relationship; two-way transitivetrust.extended ASCII character set SeeASCII extended character set.Extended Binary Coded Decimal Inter-change Code Abbreviated EBCDIC;pronounced “eb-se-dic.” EBCDIC is thecharacter set commonly used on large IBMmainframe computers, most IBM minicom-puters, and computers from many othermanufacturers.It is an 8-bit code, allowing 256 differentcharacters (see Appendix D). Unlike ASCII,the placement of the letters of the alphabetin EBCDIC is discontinuous. Also, there isno direct character-to-character matchwhen converting from EBCDIC to ASCII;some characters exist in one set but not inthe other.See also American Standard Code for In-formation Interchange; double-byte char-acter set; ISO 10646; Unicode.Extended Industry StandardArchitecture Abbreviated EISA, pro-nounced “ee-sah.” A PC bus standard thatextends the traditional AT-bus to 32 bitsand allows more than one processor toshare the bus.EISA was developed by the so-called Gang ofNine (AST Research, Compaq ComputerCorporation,Epson,Hewlett-Packard,NEC,Olivetti, Tandy, Wyse Technology, and Ze-nithDataSystems)inreplytoIBM’sintroduc-tion of its proprietary MCA (Microchannel2461book Page 137 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 143. extended LAN138Architecture). EISA maintains compatibilitywith the earlier ISA (Industry Standard Archi-tecture), and it also provides for additionalfeatures introduced by IBM in the MCA stan-dard. EISA accepts ISA expansion cards andso, unlike MCA, is compatible with earliersystems.EISAhasbeeneclipsedbyPeripheralControl Interconnect-based systems.See also local bus; PCI local bus; PC Mem-ory Card International Association.extended LAN A term used to describe anetwork that consists of a series of LANsconnected by bridges.extended memory Memory beyond1MB on computers using the Intel 80286and later processors, not configured for ex-panded memory.PCs based on the early Intel processorscould access only 1MB of memory, ofwhich 640KB was available for applica-tions, and the remaining 384KB was re-served for MS-DOS, the BIOS, and videosettings.Later processors can access more memory,but it was the 80386 with its ability to ad-dress 4GB of memory that really made ex-tended memory usable. Also, MicrosoftWindows and other operating systems run-ning on Intel processors using the protectedmode of the 80386 and later processors canaccess all the available system memory inthe same way.extended memory manager A devicedriver that supports the software portion ofthe Extended Memory Specification in anIBM-compatible computer.Extended Memory Specification Ab-breviated XMS. A standard developed byMicrosoft, Intel, Lotus, and AST Researchthat became the preferred way of accessingextended memory in the PC. MS-DOS in-cludes the extended memory device driverHIMEM.SYS, and this command or anequivalent must be present in CONFIG.SYSto allow you to access extended memory.Extensible Authentication ProtocolAbbreviated EAP. In Microsoft Windows2000 Server, a mechanism that allows fu-ture authentication schemes to be added tothe operating system quickly and easily.See also Challenge-Handshake Authenti-cation Protocol.Extensible Markup Language Abbre-viated XML. A technology, based on Stan-dard Generalized Markup Language(SGML), that allows the data on a Hyper-Text Markup Language (HTML) page tobe described in terms of the information itrepresents.See also document type definition; Hyper-Text Markup Language.external command A command that isa separate program, and not built in to theoperating system. FORMAT, BACKUP,and FDISK are examples of externalcommands.See also internal command.External Gateway Protocol Abbrevi-ated EGP. A routing protocol used to ex-change network availability informationamong organizational networks. EGP indi-cates whether a given network is reachable,2461book Page 138 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 144. 139extremely low-frequency emissionbut it does not evaluate that information ormake routing or priority decisions.See also Border Gateway Protocol.external modem A stand-alone mo-dem, separate from the computer and con-nected to it by a serial cable. LEDs on thefront of the chassis indicate the current mo-dem status. An external modem can be usedwith different computers at different timesand also with different types of computers.external reference In Novell NetWare,a pointer to a NetWare Directory Services(NDS) object that is not located on the cur-rent server.extranet Originally coined as a term todescribe any network in which part of thenetwork was protected behind a firewalland part of the network was accessible fromthe Internet.In current usage, an extranet describes atechnology that allows different corporateintranets to communicate for the purposesof electronic commerce and collaboration.Those parts of an extranet outside the fire-wall contain their own set of security safe-guards, allowing only limited access forspecific purposes.See also intranet.extremely low-frequency emissionAbbreviated ELF. Radiation emitted by acomputer monitor and other common elec-trical appliances.ELF emissions fall into the range of 5 to2000 hertz and decline with the square ofthe distance from the source. Emissions arenot constant around a monitor; they arehigher from the sides and rear and weakestfrom the front of the screen. Low-emissionmodels are available, and laptop computerswith an LCD display do not emit any ELFfields.See also electromagnetic interference;radio frequency interference; very low-frequency emission.2461book Page 139 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 145. facsimile140Ffacsimile See fax.fading In both electrical and wireless sys-tems, a decrease in a signal’s strength.Fading may be due to physical obstructionsof the transmitter or receiver, to distancefrom the source of the transmission, or tosome form of external interference from oth-er signals or from atmospheric system Any computer systemthat is designed to keep operating, withoutlosing data, when part of the system seri-ously malfunctions or fails system Any computer systemthat is designed to fail gracefully, with theminimum amount of data or program de-struction, when part of the system malfunc-tions. Fail-soft systems close down non-essential functions and operate at a reducedcapacity until the problem is resolved.fake root A subdirectory that functionsas the root directory.Fake roots can be useful with network ap-plications that must be installed in the rootdirectory. You can install the application ina subdirectory and then map a fake root onthe file server to the subdirectory contain-ing the application. Many Web servers usea fake root.fall back A technique used by modems toadjust their data rate in response to chang-ing line conditions.FAQ See frequently asked questions.far-end crosstalk Abbreviated FEXT.Interference that occurs when signals onone twisted-pair are coupled with anotherpair as they arrive at the far end of a multi-pair cable system.FEXT becomes a problem on short loopssupportinghigh-bandwidthservicessuchasVery-High-Bit-RateDigitalSubscriberLine(VDSL) because of the high carrier frequen-cies used.See also crosstalk; near-end crosstalk.Fast Ethernet A term applied to theIEEE 802.3 Higher Speed Ethernet StudyGroup proposals, which were originally de-veloped by Grand Junction Networks,3Com, SynOptics, Intel, and others. Alsoknown as 100BaseT.Fast Ethernet modifies the existing Ethernetstandard to allow speeds of 10Mbps or100Mbps or both and uses the CSMA/CDaccess method.The official standard defines three physical-layer specifications for different cablingtypes:I100BaseTX for two-pair Category 5 un-shielded twisted-pairI100BaseT4 for four-pair Category 3, 4, or5 unshielded twisted-pairI100BaseFX for fiber-optic cableSee also 100VG-AnyLAN; demand priority.Fast IP A technology from 3Com Corpo-ration that gives certain types of network2461book Page 140 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 146. 141fault tolerancetraffic, such as real-time video, a higher pri-ority than other, less urgent network trafficsuch as e-mail messages.3Com achieves this using what it calls pol-icy management. A workstation requests acertain level of priority, tags the data ac-cordingly, and begins the transmission.When the transmission is complete, theworkstation indicates that to the network,and previously reserved resources are freedup for use.See also IP over ATM; IP switching; qualityof service.Fast IR A 4Mbps extension to the SerialInfrared Data Link Standard that provideswireless data transmission between IrDA-compliant devices.See also Infrared Data Association.Fast SCSI A version of the SCSI-2 inter-face that can transfer data 8 bits at a time atdata rates of up to 10MBps. The Fast SCSIconnector has 50 pins.See also Fast/Wide SCSI; SCSI-2; SmallComputer System Interface; Ultra SCSI;Ultra Wide SCSI; Wide SCSI.Fast/Wide SCSI A version of the SCSI-2interface that can transfer data 16 bits at atime at data rates of up to 20MBps. TheFast/Wide SCSI connector has 50 pins.See also Fast SCSI; SCSI-2; Small Comput-er System Interface; Ultra SCSI; Ultra WideSCSI; Wide SCSI.FAT See file allocation table.FAT16 In Microsoft Windows, a fileallocation table that uses a 16-bit clusteraddressing scheme which restricts themaximum hard-disk size to 2.6GB. Also,FAT16 is inefficient in disk-space utiliza-tion as the default cluster size can be aslarge as 32KB.See also FAT32; file allocation table.FAT32 In Microsoft Windows 95 (release2) and later versions of Windows, a file al-location table that uses a 32-bit cluster ad-dressing scheme to support hard diskslarger than 2.6GB, as well as a default clus-ter size of as small as 4KB. FAT32 can sup-port hard disks of up to 2 terabytes in size.See also FAT16; file allocation table.fatal error An operating system or appli-cation program error from which there isno recovery without reloading the programor rebooting the operating system.fault management One of the five basictypes of network management defined bythe International Organization for Stan-dardization (ISO) and CCITT. Fault man-agement is used in detecting, isolating, andcorrecting faults on the network.fault tolerance A design method that en-sures continued system operation in theevent of individual failures by providing re-dundant elements.At the component level, the design includesredundant chips and circuits and the capa-bility to bypass faults automatically. At thecomputer-system level, any elements thatare likely to fail, such as processors andlarge disk drives, are replicated.Fault-tolerant operations often requirebackup or UPS (uninterruptible power2461book Page 141 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 147. fax142supply) systems in the event of a mainpower failure. In some cases, the entirecomputer system is duplicated in a remotelocation to protect against vandalism, actsof war, or natural disaster.See also clustering; data protection; diskduplexing; disk mirroring; redundant ar-ray of inexpensive disks; System FaultTolerance.fax Short for facsimile. The electronictransmission of copies of documents for re-production at a remote location. The termfax can be used as a verb for the process andas a noun for the machine that does thework and also for the item that is actuallytransmitted.The sending fax machine scans a paper im-age and converts the image into a form suit-able for transmission over a telephone line.The receiving fax machine decodes andprints a copy of the original image. Each faxmachine includes a scanner, modem, andprinter.Originally, facsimile machines were rotat-ing drums (CCITT Groups 1 and 2); thencame modems (CCITT Group 3), and even-tually they will be completely digital(CCITT Group 4).See also CCITT Groups 1–4; fax modem.fax board See fax modem.fax modem An adapter that fits into aPC expansion slot providing many of thecapabilities of a full-sized fax machine, butat a fraction of the cost. Some external mo-dems also have fax capabilities.The advantages of a fax modem includeease of use and convenience; the main dis-advantage is that the material you want tofax must be present in digital form in thecomputer. Unless you have access to a scan-ner, you cannot fax handwritten notes, lineart, or certain kinds of graphics. Most faxessent directly from a PC using a fax modemare text files.fax server A dedicated server that pro-vides fax sending and receiving services tousers on the network.FCC See Federal CommunicationsCommission.FCC certification Approval by the FCC(Federal Communications Commission)that a specific computer model meets itsstandards for radio frequency interference(RFI) emissions. There are two levels ofcertification:IClass A certification, which is for comput-ers used in commercial settings, such asmainframes and minicomputersIThe more stringent Class B certification,which is for computers used in the homeand in home offices, such as PCs, laptops,and portablesSee also extremely low-frequency emis-sion; radio frequency interference; verylow-frequency emission.FDDI See Fiber Distributed DataInterface.FDDI-II A variation of the Fiber Distrib-uted Data Interface standard. The FDDI-IIversion is designed for networks transmit-ting real-time full-motion video (or other2461book Page 142 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 148. 143Fiber Distributed Data Interfaceinformation that cannot tolerate any de-lays) and requires that all nodes on the net-work use FDDI-II; otherwise, the networkautomatically reverts to FDDI.FDDI-II divides the bandwidth into 16 ded-icated circuits operating at from 6.144Mbpsto a maximum of 99.072Mbps. Each ofthese channels can be further subdivided fora total of 96 separate 64Kbps circuits.FDDI-II is not widely used because it is in-compatible with FDDI and because FastEthernetandAsynchronousTransferMode(ATM) both provide better solutions.FDM See frequency-divisionmultiplexing.FDX See full-duplex.Federal CommunicationsCommission Abbreviated FCC. A U.S.government regulatory body for radio,television, all interstate telecommunica-tions services, and all international servic-es that originate inside the United States.All computer equipment must be certifiedby the FCC before it can be offered for salein the United States. The certification en-sures that the equipment meets the legallimits for conductive and radio frequencyinterference, which could otherwise inter-fere with commercial broadcasts.For more information on the FCC, also FCC certification.female connector Any cable connectorwith receptacles designed to receive the pinson the male connector.See also male connector.FEMALE CONNECTORFEXT See far-end crosstalk.FF See form feed.Fiber Distributed Data Interface Ab-breviated FDDI. The ANSI X3T9.5 specifi-cation for fiber-optic networks transmittingat a speed of up to 100Mbps over a dual,counter rotating, token-ring topology.FDDI’s 100Mbps speed is close to the inter-nal speed of most computers, which makes ita good choice to serve as a super backbonefor linking two or more LANs or as a fiber-optic bus connecting high-performanceengineering workstations. FDDI is suited tosystems that require the transfer of largeamounts of information, such as medical2461book Page 143 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 149. fiber-optic cable144imaging, three-dimensional seismic process-ing, and oil reservoir simulation. The FDDI-II version of the standard is designed for net-workstransmittingreal-timefull-motionvid-eo (or other information that cannot tolerateany delays) and requires that all nodes on thenetworkuseFDDI-II;otherwise,thenetworkautomatically reverts to FDDI.A FDDI network using multimode fiber-optic cable can include as many as 500 sta-tions up to 2 kilometers (1.25 miles) apart;with single-mode fiber, run length increasesup to 60 kilometers (37.2 miles) betweenstations. This type of network can also runover shielded and unshielded twisted-paircabling (when it is known as CDDI, or Cop-per Distributed Data Interface) for shorterdistances.See also FDDI-II.FIBER DISTRIBUTED DATA INTERFACEfiber-optic cable A transmission tech-nology that sends pulses of light along spe-cially manufactured optical fibers.Each fiber consists of a core, thinner than ahuman hair, surrounded by a sheath with amuch lower refractive index. Light signalsintroduced at one end of the cable are con-ducted along the cable as the signals are re-flected from the sheath.Fiber-optic cable is lighter and smallerthan traditional copper cable, is immuneto electrical interference, offers better se-curity, and has better signal-transmittingqualities. However, it is more expensivethan traditional cables and is more diffi-cult to repair. Fiber-optic cable is oftenused for high-speed backbones, but asprices drop, we may even see fiber-opticcable running to the desktop.See also multimode fiber; single-modefiber.2461book Page 144 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 150. 145file allocation tableFIBER-OPTIC CABLEFibre Channel An interconnection stan-dard designed to connect peripherals, massstorage systems, archiving and imaging sys-tems, and engineering workstations.Fibre Channel provides bandwidth from100Mbps to 800Mbps over a variety of ca-ble types, including multimode fiber, coax-ial cable, and shielded twisted-pair.The Fibre Channel Interconnect Stan-dard was developed by the American Na-tional Standards Institute (ANSI) X3T9committee.file A named collection of informationthat appears to the user as a single entityand is stored on disk.A file can contain a program or part of aprogram, just data, or a user-created docu-ment. Files may actually be fragmented orstored in many different places across thedisk. The operating system manages thetask of locating all the pieces when a requestis made to read the file.file allocation table Abbreviated FAT,pronounced “fat.” A table, maintained bythe operating systems, that lists all theblocks of disk space available on a disk.The FAT includes the location of eachblock, as well as whether it is in use, avail-able for use, or damaged in some way andtherefore unavailable. Because files are notnecessarily stored in consecutive blocks on2461book Page 145 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 151. file compression146a disk, the FAT also keeps track of whichpieces belong to which file.See also FAT16; FAT32; file fragmentation.file compression A technique thatshrinks program or data files so that theyoccupy less disk space. The file must then beextracted or decompressed before use.Some types of files, such as word processordocuments, can be compressed by 50 per-cent or more. Recompressing an alreadycompressed file usually makes the fileslightly larger because of the compressionoverhead.File compression can be automatic andperformed by the operating system, or itcan be manual and performed by a file-compression program.See also file-compression program.file-compression program An applica-tion that compresses files so that they takeup less space on the disk. Some file-com-pression programs are individual, stand-alone applications; others are built into theoperating system.Individual file-compression programs cancompress one or more files at a time. Theutilities PKZIP and WinZip (for MicrosoftWindows) and StuffIt (for the Macintosh)operate that way. When compression isbuilt into the operating system, it usuallycompresses all the files on a specific disk,disk partition, or volume.Many of the stand-alone file-compressionprograms, such as PKZIP, LHArc, andStuffIt, are available as shareware, andmany popular utility packages, such as theNorton Utilities from Symantec, also con-tain file-compression programs.file-conversion program An applica-tion that converts a file from one format toanother without altering the contents of thefile.The conversion may be between the formatsof two applications that use the same oper-ating system (such as between two differentMicrosoft Windows word processors) or be-tween the formats of applications from dif-ferent operating systems. Applications arealso available that convert a graphical imagefrom one file format to another.Many of the applications that change aMacintosh file into a PC-compatible file, orvice versa, consist of two programs runningsimultaneously on two physically connect-ed computers. MacLink Plus from Data Vizand LapLink Mac from Traveling Softwareare two examples of this type of file-conver-sion program.file format A file structure that definesthe way information is stored in the file andhow the file appears on the screen or on theprinter.The simplest file format is a plain ASCII file.Some of the more complex formats areDCA (Document Content Architecture)and RTF (Rich Text Format), which in-clude control information for use by aprinter; TIFF (Tagged Image File Format)and EPS (Encapsulated PostScript), whichhold graphics information; and DBF(Xbasedatabasefile)andDB(Paradoxfile),which are database formats. Word process-ingprograms,suchasMicrosoftWord,alsocreate files in special formats.2461book Page 146 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 152. 147file permissionsfile fragmentation Storage of files inpieces scattered on a disk. As files grow ona hard disk, they can be divided into sev-eral small pieces. By fragmenting files, theoperating system makes reasonable use ofthe disk space available. The problem withfile fragmentation is that the disk headsmust move to different locations on thedisk to read or write to a fragmented file.This process takes more time than readingthe file as a single piece. To speed up fileoperations, you can use a disk optimizer ordefragmenter.See also FAT16; FAT32; defragmenter.file indexing A technique used in NovellNetWare to speed up accesses to large filesby indexing file allocation table (FAT)entries.file-infecting virus Any virus that in-fects files on disk, usually executable fileswith filename extensions of .COM, .EXE,and .OVL. An unexpected change in the filesize may indicate an infection. In certaincases, the original program is replaced witha new file containing an infected program.See also antivirus program; boot sector vi-rus; infection; macro virus; multipart virus;polymorphic virus; stealth virus; TrojanHorse; vaccine; virus.file locking See file and record locking.filename The name of a file on a diskused so that both you and the operating sys-tem can find the file again. Every file in a di-rectory must have a unique name, but filesin different directories can share the samename.In MS-DOS, file and directory names havetwo parts. They can have up to eight char-acters in the name and up to three charac-ters in the optional filename extension,separated from the name by a period. Manyapplications take over the extension part ofthe filename, using specific groups of char-acters to designate a particular file type.IntheMacintoshoperatingsystem,filenamescan be up to 32 characters and can containanycharacterexceptacolon(:),whichisusedto separate elements of a path name.Microsoft Windows allows 255-characterfilenames including spaces, but the namecannot include any of the following charac-ters: / : * ? ” < > |.filename extension In the MS-DOS fileallocation table (FAT) file system, an op-tional three-character suffix added to theend of a filename and separated from thename by a period.file permissions A set of permissions as-sociated with a file (or a directory) thatspecifies who can access the file and in whatway. There are three basic permissions:IRead permission lets you read files.IWrite permission lets you write (or over-write) files.IExecute permission lets you execute files.Additional file permissions vary accordingto the operating system in use and the secu-rity system in place. For example, NovellNetWarehasthefollowingfilepermissions:Access Control, Create, Erase, File Scan,Modify, Read, Supervisor, and Write. Mi-crosoft Windows 2000 has Add and Read,2461book Page 147 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 153. File and Print Services for NetWare148Change Permissions, Delete, Full Control,No Access, and Take Ownership.See also rights.File and Print Services for NetWareAn add-on product for Microsoft Windows2000 that allows Novell NetWare clients toaccess Windows servers as though theywere NetWare servers.FILER A Novell NetWare workstationutility used to manage the NetWare file sys-tem. Almost any task related to the file sys-tem can be performed using FILER. Admin-istrators can view information about files,directories, and volumes; modify and viewattributes, rights, and trustee assignmentsfor files and directories; search for files anddirectories;copyfiles;andrecoverandpurgedeleted files. In NetWare 3.x, these last twofunctions are found in the SALVAGE andPURGE commands.file and record locking A method ofcontrolling file access in a multiuser envi-ronment, where there is always a possibilitythat two users will attempt to update thesame file at the same time but with differentinformation. The first user to access the filelocks out all the other users, preventingthem from opening the file. After the file isupdated and closed again, the next user cangain access.File locking is a simple way to prevent simul-taneousupdates,butitcanseriouslydegradesystemperformanceifmanyusersattempttoaccess the same files time after time. To pre-vent this slowdown, many database man-agement systems use record locking instead.Record locking limits access to individualrecords within the database file.file recovery The process of recoveringdeleted or damaged files from a disk. A filecan be deleted accidentally or can becomeinaccessible when part of the file’s controlinformation is lost. In many operating sys-tems, a deleted file still exists on disk untilthe space it occupies is overwritten withsomething else or until the file is purged.See also undelete.File Replication Service In MicrosoftWindows 2000 Server, the replacement forWindows NT Directory Replication.File Replication Service log In Mi-crosoft Windows 2000 Server, a special logthat records any events associated with do-main controller updates.Seealso DirectoryServicelog;DNSServerlog; Event Viewer; File Replication Service.file server A networked computer usedto store files for access by other client com-puters on the network.On larger networks, the file server runs aspecial network operating system. Onsmaller installations, the file server may runa PC operating system supplemented bypeer-to-peer networking software.See also client; server.file sharing The sharing of files over anetwork or between several applicationsrunning on the same workstation.Shared files can be read, reviewed, and up-datedbymorethanoneindividual.Accesstothefileorfilesisoftenregulatedbypasswordprotection, account or security clearance, orfile locking to prevent simultaneous changesby multiple users.2461book Page 148 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 154. 149fingerSee also file and record locking.filespec A contraction of file specifica-tion, commonly used to denote the com-plete drive letter, path name, directoryname, and filename needed to access a spe-cific file.file system In an operating system, thestructure by which files are organized,stored, and named.Some file systems are built-in components ofthe operating system; others are installable.For example, OS/2, Unix, and MicrosoftWindows are all capable of supporting sev-eral different file systems at the same time.Other, installable file systems provide sup-portforspecificdevicessuchasCD-ROMorDVD.File Transfer Access and Manage-ment Abbreviated FTAM. The OpenSystems Interconnect (OSI) protocol fortransferring and remotely accessing files ondifferent makes and models of computersthat are also using FTAM.file-transfer program An applicationused to move a file from a computer of onetype to a computer of another type. The fileformat itself may also be changed duringthis transfer.Many of the applications that change aMacintosh file into a PC-compatible file, orvice versa, consist of two programs runningsimultaneously on two physically connect-ed computers. MacLink Plus from Data Vizand LapLink Mac from Traveling Softwareare two file-transfer programs that also of-fer a wide variety of popular file-formatconversions.See also file-conversion program; FileTransfer Protocol; Kermit; Xmodem; Ymo-dem; Zmodem.File Transfer Protocol AbbreviatedFTP. The TCP/IP Internet protocol usedwhen transferring single or multiple filesfrom one computer system to another.FTP uses a client/server model, in which asmall client program runs on your comput-er and accesses a larger FTP server runningon an Internet host. FTP provides all thetools needed to look at directories andfiles, change to other directories, andtransfer text and binary files from one sys-tem to another.See also anonymous FTP; ftp; Telnet.FILTCFG A Novell NetWare 4.x Net-Ware Loadable Module (NLM) that allowsyou to set up and configure filters for Inter-network Packet eXchange (IPX), TCP/IP,and AppleTalk protocols. Filters help tocontrol the type and amount of informationsent to and received by a router, to limittraffic to certain segments of the network,and to provide security.filtering 1. Themechanismthatpreventscertain source and destination addressesfrom crossing a bridge or router onto an-other part of the network.2. The process of automatically selectingspecific frequencies and discarding others.finger A utility found on many Internetsystems that displays information about aspecific user, including full name, logontime, and location. Originated in the Unixworld.2461book Page 149 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 155. FIRE PHASERS150The finger utility may also display the con-tents of the user’s .plan or .profile file, andthere are those who exploit this in novelways to display such varied information asinstructions for using a university’s Coke-vending machine, posting sports scores,and listing earthquake activity.FIRE PHASERS ANovellNetWareloginscript command that makes a noise usingthe workstation’s speaker.The sound is supposed to resemble thephasers on the USS Enterprise. With firephasers, you can have the computer emit upto nine sounds or blasts.firewall A barrier established in hard-ware or in software, or sometimes in both,that monitors and controls the flow of traf-fic between two networks, usually a privateLAN and the Internet.A firewall provides a single point of entrywhere security can be concentrated. It al-lows access to the Internet from within theorganization and provides tightly con-trolled access from the Internet to resourceson the organization’s internal network.See also application-level filter; dual-homed host; Intrusion Detection System;packet-level filter; proxy server; statelessfilter.FireWire See 1394.firmware Any software stored in a formof read-only memory (ROM), erasable pro-grammable read-only memory (EPROM),or electrically erasable programmable read-only memory (EEPROM) that maintains itscontents when power is removed.first-layer domain In Microsoft Win-dows 2000 Server, a Windows 2000 do-main whose parent domain is the rootdomain.See also domain; parent domain.flame A deliberately insulting e-mailmessage or post to a Usenet newsgroup, of-ten containing a personal attack on thewriter of an earlier post.See also flame bait; flame war.flame bait An insulting or outrageouse-mailposttoaUsenetnewsgroupspecificallydesigned to provoke other users into flamingthe originator.See also flame; flame war.flame war In a Usenet newsgroup, a pro-longed series of flames, which may have be-gun as a creative exchange of views butwhich quickly descended into personal at-tacks and crude name-calling.See also flame bait.flash memory A special form of ROMthat can be erased at signal levels commonlyfound inside the PC.This ability allows the contents to be repro-grammed without removing the chips fromthe computer. Also, once flash memory hasbeen programmed, you can remove the ex-pansion board it is mounted on and plug itinto another computer without loss of thenew information.See also PC Card.flavor A slang expression meaning typeor kind, as in “Unix comes in a variety offlavors.”2461book Page 150 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 156. 151forestfloating-point processor A special-purpose, secondary processor designed toperform floating-point calculations muchfaster than the main processor.Many processors, such as the Intel 80386,had matched companion floating-pointprocessors. However, the current trend inprocessor design is to integrate the floating-point unit into the main processor, as in theIntel Pentium.flooding A denial of service attack inwhich a huge number of nuisance connec-tion attempts are made in order to consumeall the available processing time.See also brute-force attack; denial of ser-vice attack; dictionary attack; social engi-neering; Trojan Horse.flow control 1. In communications,control of the rate at which information isexchanged between two computers over atransmission channel. Flow control is need-ed when one of the devices cannot receivethe information at the same rate as it can besent, usually because some processing is re-quired on the receiving end before the nexttransmission unit can be accepted. Flowcontrol can be implemented either in hard-ware or in software.2. In networking, control of the flow ofdata throughout the network, ensuring thatnetwork segments are not congested. Aroutercontrolsdataflowbyroutingaroundany trouble spots.See also handshaking.followup A reply to a post in a Usenetnewsgroup or to an e-mail message. A fol-lowup post may quote the original post sothat other readers are reminded of the dis-cussion so far, and this quoted part of thepost is usually indicated by greater thansymbols (>). If you do quote from a previ-ous post, only quote the minimum amountto get your point across; never quote thewhole message as this is considered a wasteof time and resources.See also thread.footprint The amount of desktop spaceor floor space occupied by a computer,printer, or monitor.forced perfect termination A tech-nique used to terminate a Small ComputerSystem Interface (SCSI). Forced perfect ter-mination actively monitors the bus to en-sure that no signal reflection occurs.See also active termination; passivetermination.foreground In an operating system, aprocess that runs in the foreground is run-ning at a higher level of priority than is abackground task.Only multitasking operating systemssupport true foreground and backgroundprocessing; however, some applicationprograms can mimic it. For example, manyword processors will print a documentwhile still accepting input from thekeyboard.See also background.forest In Microsoft Windows 2000, acollection of Active Directory trees that donot share a contiguous namespace, but doshare a common schema and global catalog.2461book Page 151 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 157. formatting152For example, if and widget.comwere linked via a trust relationship butshared a common schema and global cata-log, they would be considered a forest; inother words, a forest is a group of trees thattrust each other.See also Active Directory; Global Catalog;schema; tree.formatting The process of initializing anew, blank floppy disk or hard disk so thatit can be used to store information.form feed Abbreviated FF. A printercommand that advances the paper in theprinter to the top of the next page. TheForm Feed button on the printer also per-forms this same function. An applicationcan also issue the command. In the ASCIIcharacter set, a form feed has the decimalvalue of 12.forward error correction A techniqueused to control errors that insert extra or re-dundant bits into the data stream. The re-ceiving device uses the redundant bits todetect and, if possible, correct the errors inthe data.See also error detection and correction.forwarding The process of passing dataon to an intermediate or final destination.Forwarding takes place in network bridges,routers, and gateways.four-wire circuit A transmission systemin which two half-duplex circuits, consist-ing of two wires each, are combined to cre-ate one full-duplex circuit.fps See frames per second.FQDN See fully qualified domain name.fractional T1 One portion of a T1 circuit.A T1 circuit has a capacity of 1.544Mbps,the equivalent of twenty-four 64Kbps chan-nels. Customers can lease as many of these64Kbps channels as they need; they are notrequired to lease the entire 1.544Mbpscircuit.fragmentation See file fragmentation.frame 1. A block of data suitable fortransmission as a single unit; also referredto as a packet or a block. Some media cansupport multiple frame formats.2. In digital video, one screen of informa-tion, including both text and graphics.See also frames per second.frame relay A CCITT standard for apacket-switching protocol, running atspeeds of up to 2Mbps, that also providesfor bandwidth on demand. Frame relay isless robust than X.25 but provides better ef-ficiency and higher throughput.Frame relay is available from many compa-nies, including AT&T, CompuServe,Sprint, WilTel, and the Bell companies.See also Asynchronous Transfer Mode.frames per second Abbreviated fps.The number of video frames displayed eachsecond. Although 24fps is considered theslowest frame rate that provides convincingmotion to the human eye, most Internet vid-eo runs at between 5 and 15fps. To main-tain a 15fps rate, you need a fast Pentium-based system with a 56Kbps modem.2461book Page 152 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 158. 153frequency-division multiplexingframing The process of dividing data fortransmission into groups of bits and addinga header as well as a checksum to form aframe. In asynchronous communications,framing is the process of inserting start bitsand stop bits before and after the data to betransmitted.FreeBSD A free implementation of Unixfor the Intel family of processors, derivedfrom the 4.4BSD Lite releases.The distribution is free, but there may be asmallchargetocoverthedistributionmediaand packaging. FreeBSD also includesXFree86, a port of the X Window system tothe Intel processors.Most of FreeBSD is covered by a licensethat allows redistribution as long as thecode acknowledges the copyright of theRegents of the University of California andthe FreeBSD Project. Those parts of Free-BSD that include GNU software are cov-ered separately by the Free Software Foun-dation license.See also copy left; Free Software Founda-tion; freeware; GNU; Linux; open memory Any area of memory notcurrently in use. Often refers to the memoryspace remaining for applications to use af-ter the operating system and the system de-vice drivers have been loaded.Free Software Foundation Abbreviat-ed FSF. An organization founded by Rich-ard Stallman that develops the freelyavailable GNU software.The FSF philosophy is that all softwareshould be free for everyone to use and thatsource code should always accompany thesoftware. The theory being, that if youmake a modification or fix an error, thechange can be sent out to all the other users,saving time and preventing duplication ofeffort.Also, any software developed under the FSFGeneral Public License (GPL) must also becovered by the same terms of the GPL; inother words, you cannot use the free soft-ware to develop a commercial product forsale.For more information on the Free SoftwareFoundation, see also copy left; FreeBSD; freeware;GNU; open source software.freeware A form of software distribu-tion in which the author retains copyrightto the software, but makes the programavailable to others at no cost. The programcannot be resold by a third party for profit.See also copy left; Free Software Founda-tion; GNU; open source software.frequency-division multiplexing Ab-breviated FDM. A method of sharing atransmission channel by dividing the band-width into several parallel paths, definedand separated by guard bands of differentfrequencies designed to minimize interfer-ence. All signals are carried simultaneously.FDM is used in analog transmissions, suchas in communications over a telephone line.See also inverse multiplexing; statisticalmultiplexing; time-division multiplexing;wavelength division multiplexing.2461book Page 153 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 159. frequently asked questions154frequently asked questions Abbrevi-ated FAQ, pronounced “fack.” A docu-ment that contains answers to questionsthat new users often ask when they firstsubscribe to a newsgroup or first access aWeb site.The FAQ contains answers to commonquestions that the seasoned users havegrown tired of answering. New usersshould look for and read the FAQ beforeposting their question, just in case the FAQcontains the answer.fried A slang expression for burned-outhardware, especially hardware that has suf-fered from a power surge. Also applied topeople, as in “My brain is fried; I haven’tslept since last weekend.”front-end application An applicationrunning on a networked workstation thatworks in conjunction with a back-end sys-tem running on the server. Examples are e-mail and database programs.See also client/server architecture.front-end processor A specialized pro-cessor that manipulates data before passingit on to the main processor.In large computer-to-computer communi-cations systems, a front-end processor isoften used to manage all aspects of com-munications, leaving the main computerfree to handle the data processing.See also back-end processor.FRS See File Replication Service.Frye Utilities A package of network man-agement utilities from Frye Computer Sys-tems that includes hardware and softwareinventory, NetWare server monitoring, traf-fic monitoring, application metering, andsoftware distribution.FSF See Free Software Foundation.FTAM See File Transfer Access andManagement.FTP See File Transfer Protocol.ftp A command used to transfer files toand from remote computers using the FileTransfer Protocol. You can use ftp to log onto an Internet computer and transfer textand binary files.When you use ftp, you start a client pro-gram on your computer that connects to aserver program on the Internet computer.The commands that you give to ftp aretranslated into instructions that the serverprogram executes for you.The original ftp program started life as aUnix utility, but versions are now availablefor all popular operating systems; ftp is alsobuilt into all the major Web browsers.See also anonymous ftp; File TransferProtocol.full backup A backup that includes allfiles on a hard disk or set of hard disks. Anetwork administrator must decide how of-ten to perform a full backup, balancing theneed for security against the time taken forthe backup.See also differential backup; incrementalbackup.2461book Page 154 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 160. 155function keysfull-duplex Abbreviated FDX. The capa-bility for simultaneous transmission in twodirections so that devices can be sendingand receiving data at the same time.See also four-wire circuit; half-duplex.full-page display Any monitor capableof displaying a whole page of text. Full-page displays are useful for graphical artand desktop publishing applications, aswell as medical applications.fully qualified domain name A hostname with the appropriate domain name ap-pended.Forexample,onahostwiththehostname wallaby and the Domain Name Ser-vice (DNS) domain name,the fully qualified domain name also Domain Name Service.function keys The set of programmablekeys on the keyboard that can performspecial tasks assigned by the currentapplication.Most keyboards have 10 or 12 functionkeys (F1 to F10 or F1 to F12), some ofwhich are used by an application as short-cut keys. For example, many programs useF1 to gain access to the Help system. Insome programs, the use of function keys isso complex that special plastic key overlaysare provided as guides for users.2461book Page 155 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 161. G156GG Abbreviation for giga-, meaning 1 bil-lion, or 109.See also gigabyte.Gartner Group, Inc. An independentresearch organization for the computerhardware, software, communications, andrelated industries.Gartner Group first developed the conceptof total cost of ownership (TCO) and nowprovides TCO software tools since the ac-quisition of Interpose. Gartner Group alsoowns Datapro Information Services and themarket analysis company Dataquest.For more information on Gartner Group,see also total cost of ownership.gate array See application-specificintegrated circuit.gateway A shared connection between aLAN and a larger system, such as a main-frame computer or a large packet-switchingnetwork,whosecommunicationsprotocolsare different. Usually slower than a bridgeor router, a gateway is a combination ofhardware and software with its own pro-cessor and memory used to perform proto-col conversions.See also bridge; brouter; router.Gateway, Inc. Aleadingdirect-marketerof PCs, servers, and related peripherals,originally known as Gateway 2000. Alsoan ISP offering Internet access more information on Gateway, Inc., server A communicationsserver that provides access between net-works that use different access protocols.Gateway Services for NetWare A Mi-crosoft Windows NT Server service that al-lows an NT server to act as a gateway to aNetWare network. NT clients can access aNetWare server using the same methodsused to access an NT server.gauge A measurement of the physicalsize of a cable. Under the American WireGauge (AWG) standards, higher numbersindicate thinner cable.See also cabling standards.GB See gigabyte.Gb See gigabit.Gbit See gigabit.GDS See Global Directory Service.gender changer A special intermediaryconnector for use with two cables that bothhave only male connectors or only femaleconnectors.2461book Page 156 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 162. 157global accountGENDER CHANGERgeostationary Also known as geosyn-chronous. The type of orbit required tokeep a communications satellite in a fixedposition relative to the earth.The satellites angular rate and direction ofrotation are matched to those of the earth,and the satellite orbits the earth every 24hours at about 36,000 kilometers (22,350miles). Three satellites in geostationary or-bit can cover 95 percent of the earths sur-face (the remaining 5 percent is above theArctic Circle).geosynchronous See geostationary.GIF See Graphics Interchange Format.giga- A prefix meaning 1 billion, or 109.See also gigabyte.gigabit Abbreviated Gbit and Gb. Usu-ally 1,073,824 binary digits or bits of data.Sometimes used as equivalent to one bil-lion bits.See also kilobit; megabit.Gigabit Ethernet A1Gbps(1,000Mbps)extension of the IEEE 802.3 Ethernet stan-dard, known as 1000Base-X.This standard has been developed by theIEEE 802.3z Task Group and a number ofinterested companies collectively known asthe Gigabit Ethernet Alliance. GigabitEthernet runs over multimode fiber-opticcable and is intended for use as a backboneand a way to connect high-speed routers,switches, and hubs.See also Ethernet; Fast Ethernet.gigabyte Abbreviated GB. Strictlyspeaking, one billion bytes; however, incomputing, in which bytes are most oftencounted in powers of 2, a gigabyte becomes230, or 1,073,741,824 account In Microsoft WindowsNT Server, a user or group account definedon a primary domain controller that can beused from all the computers in the domain.2461book Page 157 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 163. Global Catalog158Global Catalog In Microsoft Active Di-rectory, the storage of selected propertiesfor all the objects in the Active Directory.The Global Catalog allows users in an or-ganization with multiple sites to locate re-sources quickly, without having to crossWAN links. In this way, users can examinea local source to find the location of a net-work resource.See also Active Directory; forest; tree.Global Directory Service AbbreviatedGDS. An implementation of the X.500 di-rectory service for managing remote usersand addresses.See also directory services Directoryservices that view the entire network as asingle entity. A global directory system al-lows the network administrator to defineall network resources—users, printers, andservers—at one time.Banyans StreetTalk and Novells NetWareDirectory Services (NDS) are examples ofglobal directory services.See also domain directory group InMicrosoftWindowsNTServer, user accounts granted server andworkstation rights in their own and otherdomains whose security systems allow ac-cess. Global groups are a means of provid-ing rights and permissions to resourcesinside and outside the domain to a group ofusers within a single domain.See also local login A mechanism that permitsusers to log on to the network, rather thanrepeatedly logging on to individual servers.A global logon can provide access to all net-work resources.globally unique identifier AbbreviatedGUID. In Microsoft Active Directory, aunique 128-bit number that identifies anActive Directory object.See also Active network An international net-work that spans all departments, offices,and subsidiaries of the corporation.Global networks bring their own set ofproblems, including those of different timezones, languages, established standards,and PTT (Postal Telephone and Telegraph)companies.GNU Pronounced “ga-noo.” A Free Soft-ware Foundation (FSF) project devoted todeveloping a complete, freely availableUnix system that contains no AT&T code.The name GNU is a recursive acronym for“GNU’s not Unix!”Many of the tools and utilities developedfor this project have been released and arevery popular with users of 4.4BSD, Free-BSD, and Linux.For more information on GNU, also 4.4BSD Lite; FreeBSD; Hurd;Linux; open source software.Gopher A client/server application thatpresents Internet text resources as a seriesof menus, shielding the user from the2461book Page 158 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 164. 159graphics accelerator boardunderlying mechanical details of IPaddresses and different access methods.Gopher menus may contain documents youcan view or download, searches you canperform, or additional menu selections.When you choose one of these items, Go-pher does whatever is necessary to obtainthe resource you requested, either by down-loading a document or by jumping to the se-lected Gopher server and presenting its top-level menu.Gopher clients are available for most pop-ular operating systems, including the Mac-intosh, MS-DOS, Windows, and Unix.See also Gopherspace; World Wide Web.Gopherspace A collective term used todescribe all the Internet resources accessibleusing Gopher. Gopher is so good at hidingthe mechanical details of the Internet thatthis term was coined to represent all the re-sources reachable using Gopher.GOSIP Acronym formed from Govern-ment Open System Interconnection Profile.A suite of standards intended for use in gov-ernment projects and based on the OpenSystems Interconnect (OSI) reference mod-el. Some measure of GOSIP compliance isrequired for government networking pur-chases. GOSIPs exist in many countries,including the United States, Canada,France, Germany, Australia, and the Unit-ed Kingdom.GPO See group policy object.grace login Allows a user to finish log-ging on using an expired password withoutchanging it. You can set the number ofgrace logons a user is allowed.graphical user interface AbbreviatedGUI, pronounced “gooey.” A graphics-based user interface that allows users to se-lect files, programs, and commands bypointing to pictorial representations on thescreen rather than by typing long, complexcommands from a command prompt.Applications execute in windows, using aconsistent set of drop-down menus, dialogboxes, and other graphical elements, suchas scroll bars and icons. This consistencyamong interface elements is a major benefitfor the user, because as soon as you learnhow to use the interface in one program,you can use it in all other programs runningin the same environment.The use of graphical elements in a user in-terface was pioneered at Xerox Corpora-tions Palo Alto Research Center (PARC) inthe early 1970s. Unfortunately, at that timethe hardware needed to support such a userinterface was well beyond the reach of mostusers. In 1979, Steve Jobs of Apple Com-puter visited PARC and recognized the im-portance of the user-interface work beingdone; this visit led to the development of theinterface for the ill-fated Apple Lisa com-puter, and eventually to the Apple Macin-tosh series of computers. Since then, GUIshave been developed for most accelerator board A special-ized expansion board containing a graphicscoprocessor as well as all the other circuitryfound on a video adapter. Sometimes calleda video accelerator board.2461book Page 159 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 165. graphics coprocessor160Transferring most of the graphics process-ing tasks from the main processor to thegraphics accelerator board improves sys-temperformanceconsiderably,particularlyfor Microsoft Windows coprocessor Afixed-functiongraphics chip, designed to speed up theprocessing and display of high-resolutionimages. Popular coprocessors include S3Inc’s 86C911 and Weitek’s W5086 andW5186.Graphics Interchange Format Abbre-viated GIF; pronounced “gif.” A graphicsfile format, originating on CompuServe,that results in relatively small graphics files.An image may contain as many as 256 col-ors, including a transparent color, and alossless compression method reduces thesize of the file. A graphic in this format canbe used as an inline image on a Web page.A revision of this format, known asGIF89a, adds animation features, transpar-ent backgrounds, and image interleaving.See also lossless compression; JointPhotographic Experts mode A video adapter mode inwhich everything displayed on the screen iscreated pixel by pixel. Text mode, by con-trast, uses ready-made characters from abuilt-in character set.grayed command See dimmed A collection of network userswho all have the same level of security andcan all be managed account An account containingother member accounts. All the rights andpermissions accorded to the group are alsogranted to the group members, makinggroup accounts a convenient way to pro-vide a common set of capabilities to collec-tions of user identifiers Security identifierscontaining the set of permissions granted tothe group. If a user account is part of agroup, the group identifier is appended tothat user’s security identifier, granting theuser all the permissions granted to thatgroup.See also security identifier.Group object In Novell NetWare Direc-tory Services (NDS), an object that containsa list of user object names.See also leaf object; NetWare policy In Microsoft Windows2000 Server, a central point of administra-tion, allowing administrators to install soft-ware and apply standard settings tomultiple users and computers throughoutan policy object Abbreviated GPO.In Microsoft Windows 2000 Server, a col-lection of group policy settings defined atthe local machine, site, domain, or organi-zational unit level.groupware Network software designedfor use by a group of people all working onthe same project or who need access to thesame data.2461book Page 160 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 166. 161guruSee also Lotus Notes; workflow software;workgroup.guard band A small-frequency bandused to separate multiple bands in a broad-band transmission and prevent interferencebetween the communications channels.guest account In Microsoft Windows2000, a built-in account available to userswho do not have an account on the system.Allowing people to use the guest accountmay breach company security policies.GUI See graphical user interface.GUID See globally unique An operating system expert with areputation for being helpful to other, lessknowledgeable users.2461book Page 161 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 167. H.323162HH.323 A videoconferencing standard de-veloped by the International Telecommu-nication Union (ITU) that defines video-conferencing from the desktop over LANs,intranets, and the Internet.H.323 specifies techniques for compressingand transmitting real-time voice, video, anddata between a pair of videoconferencingworkstations. It also describes signalingprotocols for managing audio and videostreams, as well as procedures for breakingdata into packets and synchronizing trans-missions across communications channels.See also Real-time Transport Protocol;T.120.hack Originally, an expedient, althoughshort-term, solution to a programmingproblem. This solution often bypassedsome of the more traditional software-development processes. Now the wordhack is often used to describe a well-craft-ed piece of work that produces just what isneeded; it does not imply malicious intentto break into other people’s systems forgain.See also hacker; kluge.hacker In the programming community,where the term originated, this term de-scribes a person who pursues knowledge ofcomputer systems for its own sake—some-one willing to “hack through” the steps ofputting together a working program.More recently, in popular culture at large,the term has come to mean a person whobreaks into other people’s computers withmalicious intent (what programmers call a“cracker”). Many countries now treat con-victed crackers in the same way that theytreat conventional breaking-and-enteringcriminals.See also intruder.HAL See Hardware Abstraction Layer.half-duplex Abbreviated HDX. In asyn-chronous transmissions, the ability totransmit on the same channel in two direc-tions, but only in one direction at a time.See also communications parameters; du-plex; full-duplex.Hamming code A forward-error correc-tion technique used to detect and correctsingle-bit errors during transmission.The Hamming code adds three verificationbits to the end of each four bits of data. Thereceiving device performs a similar processto ensure that the four data bits were re-ceived correctly and to detect any missingbits.See also error detection and correction.hand-held computer A portable com-puter that is small enough to be held in onehand, such as the enormously popularPalmPilot from 3Com Corporation.2461book Page 162 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 168. 163hard disk drivehandshaking The exchange of controlcodes or particular characters to maintainand coordinate data flow between twodevices so that data is only transmittedwhen the receiving device is ready toaccept the data.Handshaking can be implemented in eitherhardware or software, and it occurs be-tween a variety of devices. For example, thedata flow might be from one computer toanother computer or from a computer to aperipheral device, such as a modem or aprinter.See also flow control; XON/XOFF.hang 1. When a program waits for anevent that never occurs, as in “the programhangs waiting for a character from thekeyboard.”2. A slang expression used when attachinga new piece of hardware to a system, usu-ally an external device attached by one ormore cables, as in “I’m going to hang a newtape drive on the server this afternoon.”See also deadlock.hard-coded A description of softwarewritten in a way that does not allow forflexibility or future expansion. For exam-ple, when program variables are placed di-rectly in the code rather than supplied asinput from the user, the entire programmust be recompiled to change the value, anobvious waste of resources.See also hard-wired.hard disk The part of a hard disk drivethat stores data, rather than the mechanismfor reading and writing to it. Sometimescalled a platter.hard-disk controller An expansionboard that contains the necessary circuitryto control and coordinate a hard disk drive.Many hard-disk controllers can managemore than one hard disk, as well as floppydisks and tape drives. On some PCs, thehard-disk controller is built into the mother-board, and in the case of an Integrated DriveElectronics hard disk, the controlling circuit-ry is mounted on the drive itself, eliminatingthe need for a separate controller.hard disk drive A storage device thatuses a set of rotating, magnetically coateddisks called platters to store data or pro-grams. In everyday use, the termshard disk,hard disk drive, and hard drive are used in-terchangeably, because the disk and thedrive mechanism are a single unit.A typical hard-disk platter rotates at severalthousand revolutions per minute, and theread/write heads float on a cushion of airfrom 10 to 25 millionths of an inch thick sothat the heads never come into contact withthe recording surface. The whole unit is her-metically sealed to prevent airborne con-taminants from entering and interferingwith these close tolerances.Hard disks range in storage capacity from afew tens of megabytes to several terabytes.The more storage space on the disk, themore important your backup strategy be-comes. Hard disks are reliable, but they do2461book Page 163 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 169. hard-disk interface164fail, and usually at the most inconvenientmoment.See also high-capacity storage system;mini-hard disk; redundant array of inex-pensive disks; single large expensive disk.hard-disk interface A standard way ofaccessing the data stored on a hard disk. Sev-eral hard-disk interface standards haveevolved over time, including the ST506 In-terface, the Enhanced Small Device Interface(ESDI), the Integrated Drive Electronics In-terface(IDE),andtheSCSI(SmallComputerSystem Interface).See also PC Memory Card InternationalAssociation.hard-disk type A number stored in apersonal computer’s CMOS random accessmemory area that defines certain hard-diskcharacteristics, such as the number of read/write heads and the number of cylinders onthe disk. This number is not directly acces-sible from the operating system. Some PCsrequire a special configuration program toaccess the hard-disk type; others permit ac-cess via the computer’s built-in ROM BIOSsetup program.hard reset A system reset made by press-ing the computer’s Reset button or by turn-ing the power off and then on again. A hardreset is used only when the system hascrashedsobadlythatpressingCtrl+Alt+Delto reboot does not work.See also hang; deadlock.hardware All the physical electroniccomponents of a computer system, includ-ing peripheral devices, printed-circuitboards, displays, and printers. If you canstub your toe on it, it must be hardware.See also firmware; liveware; software.Hardware Abstraction Layer Abbrevi-ated HAL. The lowest level of the MicrosoftWindows NT operating system, which isspecifically tailored to the type of hardwareused in the server. If the hardware changes,changes also have to be made to the HAL.hardware address The address as-signed to a network interface card (NIC) bythe original manufacturer or by the net-work administrator if the interface card isconfigurable.This address identifies the local device ad-dress to the rest of the network and allowsmessages to find the correct destination.Also known as the physical address, mediaaccess control (MAC) address, or Ethernetaddress.Hardware Compatibility List Abbrevi-ated HCL. A list of all the hardware devic-es supported by Microsoft Windows NTand Windows 2000. Items on this list haveactually been tested and verified to workproperly withWindows.hardware dependent The requirementthat a specific hardware component bepresent for a program to work. Hardware-dependent software is often difficult tomove or port to another computer.See also hardware independent.hardware independent The ability toproduce similar results in a wide varietyof environments, without requiring the2461book Page 164 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 170. 165HDLCpresence of specific hardware. The Javaprogramming language and the PostScriptpage-description language are both exam-ples of hardware independence. Java runson a wide range of computers, from the PCto a mainframe; PostScript is used bymany printer manufacturers.See also hardware dependent.hardware interrupt An interrupt or re-quest for service generated by a hardwaredevice, such as a keystroke or a tick fromthe clock. Because the processor may re-ceive several such signals simultaneously,hardware interrupts are usually assigned apriority level and processed according tothat priority.See also interrupt request; softwareinterrupt.hard-wired Describes a system designedin a way that does not allow for flexibilityor future expansion. May also refer to a de-vice that is connected directly to the net-work, such as a printer.See also hard-coded.hash function A function that maps adata item to a numeric value by use of atransformation. A hash function can con-vert a number that has meaning to a user,such as a key or other identifier, into a valuefor the location of that data in a structuresuch as a table.See also hashing; hash table.hashing The process of creating or re-creating a hash table by recalculating thesearch index code assigned to each piece ofdata in the table.See also hash function; hash table.hash table A method of representingdata so that it can be found again veryquickly.A hash table assigns a special index code toeach piece of data, and specially designedsoftware uses this code to locate the data,rather than repeating what might be a verylengthy search each time the data isrequested.See also hash function; hashing.Hayes-compatible modem Any mo-dem that recognizes the commands in theindustry-standard AT command set, origi-nally defined by Hayes MicrocomputerProducts, Inc.HBA See host bus adapter.H-channel A set of ISDN Primary RateInterface (PRI) services with predefinedspeeds, designed to carry videoconferenc-ing data streams.H-channel services are created from multi-ple 64Kbps B channels. Three service levelsare commonly available:IH0 operating at 384KbpsIH11 operating at 1,536KbpsIH12 operating at 1,920KbpsSee also Integrated Services Digital Net-work; Primary Rate ISDN.HCL See Hardware Compatibility List.HCSS See high-capacity storagesystem.HDLC See High-level Data Link Control.2461book Page 165 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 171. HDSL166HDSL See High-Bit-Rate Digital Sub-scriber Line.HDX See half-duplex.header Information placed at the begin-ning of a file, a data transmission, or anarchive.In an e-mail message, the header containsinformation about the message, includingsender and recipient information, and in-formation about the route the message tookas it was being delivered.In a data transmission, the header may con-tain source and destination address infor-mation, as well as other control data.In an archive, the header is a block that con-tains information describing the contents ofthe archive.Header Error Control In an Asynchro-nous Transfer Mode (ATM) cell header, an8-bit field used for detecting errors and cor-recting single-bit errors.See also Asynchronous Transfer Mode.headless server A server computer withno monitor attached.heartbeat An Ethernet signal quality testfunction. This signal proves that a compo-nent is working and can detect collisions.Also known as signal quality error (SQE).HEC See Header Error Control.Hello protocol In Asynchronous Trans-fer Mode (ATM), a link state protocol usedby nodes to determine who and where theirneighbors are.helper A program launched or used by aWeb browser to process a file type that thebrowser cannot handle. Sometimes called aplug-in.A helper may view an image, play a soundfile, or expand a compressed file. A helperthat deals with video, graphics, or anima-tion is called a viewer; a helper that dealswith sound files is called a player.See also player; viewer; Web browser.hertz Abbreviated Hz. A unit of frequen-cy measurement; 1 hertz equals one cycleper second.See also megahertz.heterogeneous network A networkthat consists of workstations, servers, net-workinterfacecards,operatingsystems,andapplications from many vendors, all work-ing together as a single unit. The networkmay also use different media and differentprotocols over different network links.See also enterprise network; homoge-neous network.Hewlett-Packard Company Abbreviat-ed HP. A major manufacturer of hand-heldcalculators, personal computers, servers,minicomputers, mainframes, scientific andmedical equipment, test and measurementequipment, laser and ink jet printers, plot-ters, and software.Founded by William Hewlett and DavidPackard in 1939 in a garage, the companyis now headquartered in Palo Alto, Califor-nia. HP has a widely diversified product lineof more than 10,000 items, and it has a2461book Page 166 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 172. 167High-Bit-Rate Digital Subscriber Linewell-earned reputation for building ruggedand reliable equipment.For more information on Hewlett-Packard,see See hexadecimal.hexadecimal Abbreviated hex. Thebase-16 numbering system that uses thedigits 0 through 9, followed by the letters Athrough F, which are equivalent to the dec-imal numbers 10 through 15.Hex is a convenient way to represent the bi-nary numbers that computers use internallybecause it fits neatly into the 8-bit byte. Allthe 16 hex digits 0 through F can be repre-sented in 4 bits, and 2 hex digits (1 digit foreach set of 4 bits) can be stored in a singlebyte. This means that 1 byte can containany one of 256 different hex numbers, from0 through FF.See also binary; decimal.HFS See Hierarchical File System.hidden file In many operating systems,any file that has the hidden attribute set,whichindicatestotheoperatingsystemthatinformation about the file should not ap-pearinnormaldirectorylistings.Theremayalso be further restrictions on a hidden file,and users may not be able to delete, copy, ordisplay the contents of such a file.hidden share In Microsoft Windows2000, a share whose name contains a dollarsign as the last character. The names of hid-den shares are not displayed under normalcircumstances, although they are alwaysvisible in Computer Management.See also common share; default shares;share; sharing.Hierarchical File System AbbreviatedHFS. A tree-structured file system used onthe Macintosh; designed for use with harddisks.Hierarchical Storage ManagementAbbreviated HSM. A combination of sev-eral types of file-storage systems, managedby intelligent software.In HSM, data is moved from one type ofstorage to another depending on how fre-quently the data is accessed. Active data isheld on hard disks, less frequently used datais held in near-line storage such as an opti-cal disk system, and data used only infre-quently is stored in a tape backup.See also archive; high-capacity storagesystem; jukebox.High-Bit-Rate Digital Subscriber LineAbbreviated HDSL. A high-speed datatransmission technology originally devel-oped by Bellcore that delivers high band-width over existing twisted-pair coppertelephone lines.HDSL is the most common Digital Sub-scriber Line (DSL) service and provides T1data rates of 1.544Mbps over lines of up to3.6 kilometers, or 12,000 feet, in length.HDSL is symmetric, providing the samedata rate in each direction.The service is not intended for residentialpurposes, but is used in the telephone com-pany’s own private data networks, Internetservers, and interexchange connections.See also Asymmetric Digital SubscriberLine; Digital Subscriber Line; Rate-Adaptive Digital Subscriber Line; Single-Line Digital Subscriber Line; Very-High-Bit-Rate Digital Subscriber Line.2461book Page 167 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 173. high-capacity storage system168high-capacity storage system Abbre-viated HCSS. A data-storage system thatextends the storage capacity of a NovellNetWare server by integrating an optical-disk library, or jukebox, into the NetWarefile system.Network users and applications can accessfiles and directories on the jukebox with thesame NetWare commands and functioncalls used to access files from a hard disk.The most frequently used HCSS files maybe cached temporarily on the server harddisk to speed up access times. HCSS canalso access a magnetic tape system.See also archive.high-end Anexpensive,full-featuredprod-uct from the top of a company’s product list.See also low-end.High-level Data Link Control Abbrevi-ated HDLC. An international protocol de-finedbytheISO(InternationalOrganizationfor Standardization), included in CCITTX.25packet-switchingnetworks.HDLCisabit-oriented, synchronous protocol that pro-vides error correction at the data-link layer.In HDLC, messages are transmitted in vari-able-length units known as frames.See also Synchronous Data Link Control.high-level language Any machine-independent programming language thatuses English-like syntax in which eachstatement corresponds to many assemblylanguageinstructions.High-levellanguagesfree programmers from dealing with the un-derlying machine architecture and allowthem to concentrate on the logic of theproblem at hand.See also low-level language.high memory area Abbreviated HMA.In a computer running MS-DOS, the first64KB of extended memory above the 1MBlimit of 8086 and 8088 addresses.Programs that conform to the ExtendedMemory Specification (EMS) can use thismemory as an extension of conventionalmemory. However, only one program canuse or control HMA at a time. If MS-DOSis loaded into the HMA, approximately50KB more conventional memory becomesavailable for use by applications.See also expanded memory; extendedmemory; memory management.High-Performance File System Ab-breviated HPFS. A file system available inOS/2 and Microsoft Windows NT that sup-ports the following:ILong, mixed-case filenames of up to 255charactersIAs much as 64KB of extended attributesper fileIFaster disk access with an advanced diskcache for caching files and directoryinformationIHighly contiguous file allocation thateliminates file fragmentationIHard disks of up to 64GB in sizeMS-DOS does not recognize the HPFS filestructure, it cannot be used on a floppy disk,and it is not supported in Windows NT 4 orlater.2461book Page 168 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 174. 169hiveHIGH-LEVEL DATA LINK CONTROL FRAMEHigh-Performance Parallel InterfaceAbbreviated HPPI. A parallel interfacestandard from the American National Stan-dards Institute (ANSI) known as X3T9.3,originally developed as an interface be-tween supercomputers and fast peripheralssuch as disk arrays and frame buffers.Recently, HPPI has been extended for use innetworked computers and high-end work-stations. It provides a data rate of 800Mbpsover 32-pair twisted-pair copper wire,known as single HPPI, and 1,600Mbps over64 pairs, known as double HPPI. Connec-tion length is limited to 25 meters (82 feet).High-Performance Routing Abbreviat-ed HPR. An internetworking protocol fromIBM, intended as an upgrade to its Ad-vanced Peer-to-Peer Networking (APPN)package. HPR provides internetworkingcapabilities similar to those of TCP/IP.See also Advanced Peer-to-Peer Network-ing; Data Link Switching.High Sierra specification A specifica-tion for CD-ROM data that served as thebasis for the ISO (International Organiza-tion for Standardization) 9660 standard. Itis called High Sierra because it was definedat a meeting held near Lake Tahoe in No-vember 1985.High Speed Serial Interface Abbrevi-ated HSSI. A serial data communicationsinterface optimized for speeds of up to52Mbps. Often used for connecting anAsynchronous Transfer Mode (ATM)switch to a T3 Data Service Unit.See also Asynchronous Transfer Mode;Data Service Unit; T3.hijacking An attack on a computer sys-tem in which an established TCP/IP sessionis redirected in mid-session to an unautho-rized host system.See also spoofing.hit On the World Wide Web, a requestfrom a browser for a file on the server. A hiton a Web page occurs whenever any file isaccessed, whether it is a text document, agraphic, a script, or an audio or video clip.If you access three files on a Web page, yougenerate three hits, so a hit is a poor mea-sure of the number of people visiting a Website, as it simply reflects the number of filerequests made.hive A major logical division within theMicrosoft Windows Registry. The Registryis divided into several hives:IHKEY_CLASSES_ROOT contains infor-mation about file associations.2461book Page 169 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 175. HMA170IHKEY_CURENT_USER contains infor-mation about the currently logged onuser.IHKEY_LOCAL_MACHINE contains in-formation about the computer runningWindows, including details of applica-tions, device drivers, and hardware.IHKEY_USERS contains informationabout each active user with a user profile.IHKEY_CURRENT_CONFIG containsdetails about the current systemconfiguration.IHKEY_DYN_DATA contains informa-tion about plug-and-play devices on thesystem.You can view and edit the Registry usingthe regedit.exe program.See also key; sub-key.HMA See high memory area.holy wars A fundamentally unresolv-able computer-related argument, in whichthe participants spend most of their timetrying to establish often wildly personalchoices as carefully thought out and deeplyconsidered technical evaluations. Topicsmight include any version of Unix versusany other version of Unix, the C program-ming language versus C++ (or any otherprogramming language), big endian sys-tems versus little endian systems, and so on.home directory InUnix,adirectorythatcontains the files for a specific user. Thename of your home directory is kept in thepassword file, and when you log in, yourcurrent directory is always set to be yourhome directory.home page On the World Wide Web, aninitial starting page. A home page may beprepared by an individual or by a corpora-tion and is a convenient jumping-off pointto other Web pages or Internet resources.See also portal.homogeneous network A networkthat consists of one type of workstation,server, network interface card, and operat-ing system, with a limited number of appli-cations, all purchased from a single vendor.All nodes use the same protocol and thesame control procedures.See also enterprise network; heteroge-neous network.hooked vector An intercepted interruptvector that now points to a replacement in-terrupt service routine (ISR) rather than tothe original service routine.hop A single link between two computersystems that an e-mail message must crosson its way to its destination. A message mayhave to pass over many hops to reach its ul-timate destination; if it must pass betweenfive computers, it is said to have taken fourhops to reach its destination.See also hop count.hop count In routing, the number oflinks that must be crossed to get from anygiven source node to any given destinationnode. Hop count is often used as a metricfor evaluating a route for a least-cost rout-ing algorithm.horizontal application Anyapplicationsoftware that is broad in scope and not de-signed for use in one specific industry or2461book Page 170 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 176. 171HSSIsetting. Word-processing software fallsinto this category, but software specifical-ly designed to manage a medical practicedoes not.See also vertical The central or controlling computerin a networked or distributed processingenvironment which provides services thatother computers or terminals can access viathe bus adapter Abbreviated HBA. Aboard acting as an interface between theprocessor and the hard-disk controller in anetwork server, used by Novell NetWare torelieve the main processor of data-storageand retrieval tasks. Also known as a diskcoprocessor board (DCB).The HBA and its disk subsystems make upa disk channel. NetWare can access fivedisk channels, with four controllers on eachchannel, and eight hard-disk drives at-tached to each controller.Hot Fix A Novell NetWare feature thatmarks defective disk blocks dynamically sothat the operating system will not use them.Data is redirected from any faulty blocks toa small portion of disk space set aside as theHot Fix redirection area. Hot Fix thenmarks the defective area as bad, and theserver will not attempt to store data thereagain. By default, 2 percent of a disk parti-tion is set aside as the Hot Fix redirectionarea.See also fault tolerance.HotJava A highly interactive Webbrowser from Sun Microsystems that iswritten in the Java programming language.HP See Hewlett-Packard Company.HPFS See High-Performance FileSystem.HP OpenView Certified Consultant Acertification from Hewlett-Packard thatrecognizes technical competency to bothsell and support HP OvenView, a networkmanagement system used to monitor andmanage networks consisting of equipmentand software from multiple vendors.Three specializations are available:IUnixIWindows NTIUnix and Windows NT combinedHPR See High-Performance Routing.HP-UX A version of Unix that runs onHewlett-Packard computers. HP-UX in-cludes BSD extensions, including the net-work commands, the Korn shell, and aversion of emacs. Visual User Environment(VUE) is HP’s graphical user interface, withworkspaces for different tasks, drag-and-drop functions, a text editor, a color iconeditor, and other productivity tools.HP-UX also includes System Administra-tion Manager (SAM) for common adminis-trative tasks, such as adding new users,installing and configuring peripherals,managing processes, and scheduling jobs.HSM See Hierarchical StorageManagement.HSSI See High Speed Serial Interface.2461book Page 171 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 177. HTML172HTML See HyperText MarkupLanguage.HTTP See Hypertext Transfer Protocol.hub A device used to extend a network sothat additional workstations can be at-tached. There are two main types of hubs:IActive hubs amplify transmission signalsto extend cable length and ports.IPassive hubs split the transmission signal,allowing additional workstations to beadded, usually at a loss of distance.In some star networks, a hub is the centralcontrolling device.Huffman coding In data compression, amethod of encoding data on the basis of therelativefrequencyoftheindividualelements.Huffman coding is often used with text files;the coding is based on how frequently eachletter occurs, because it is a lossless compres-sion method. Huffman coding is used in faxtransmissions.See also data compression; lossless com-pression; lossy compression.Hurd A project from the Free SoftwareFoundation (FSF) to develop and distributea free version of the Unix operating systemfor many different hardware platforms.Hurd (or sometimes HURD) is considered acollection of all the GNU software, compil-ers, editors, and utilities, as well as the op-erating system.See also Free Software Foundation; GNU.hybrid network A network that uses acollection of different technologies, such asframe relay, leased lines, and X.25.See also homogeneous network; hetero-geneous network.hybrid organization In Novell Directo-ry Services (NDS), an organizational strat-egy that combines two or more of themethods—locational, divisional, andworkgroup. A hybrid organization makesmost sense in a large organization.hypermedia A term used to describenonsequential applications that have inter-active, hypertext links between differentmultimedia elements— graphics, sound,text, animation, and video.If an application relies heavily on text-based information, it is known ashypertext; however, if full-motion video,animation, graphics, and sound are used,the application is considered hypermedia.hypertext A method of presenting infor-mation so that it can be viewed by the userin a nonsequential way, regardless of howthe topics were originally organized.Hypertext was designed to make a comput-er respond to the nonlinear way that hu-mans think and access information—byassociation, rather than according to thelinear organization of film, books, andspeech.In a hypertext application, you can browsethrough the information with considerableflexibility, choosing to follow a new patheach time you access the information. Whenyou click a highlighted word, you activate alink to another hypertext document, whichmay be on the same Internet host or on acompletely different system thousands ofmiles away. These links depend on the care2461book Page 172 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 178. 173Hzthat the document originator used when as-sembling the document; unfortunately,many links turn into dead-ends.See also link rot.HyperText Markup Language Abbre-viated HTML. A standard document for-matting language used to create Web pagesand other hypertext documents. HTML is asubset of Standardized General MarkupLanguage (SGML).HTML defines the appearance and place-ment on the page of elements such as fonts,graphics, text, links to other Web sites, andso on; it has nothing to do with the actualmaterial presented. Hypertext documentsoften have the filename extension .htm or.html.The published HTML standards have beenrevised several times. HTML version 2 wasthe first version widely used on the WorldWide Web and supported by the popularWeb browsers of the day. Subsequent revi-sions to the standard have added newHTML elements such as tables, text flowaround images, frames, applets, and stylesheets.Future HTML revisions will be developedby the World Wide Web Consortium(W3C), at least in theory; the manufactur-ers of the most popular browsers have driv-en this process in the past by creating theirown non-standard HTML elements.HTML has been vital in the development ofthe World Wide Web; however, the func-tions that it performs via the Web browserare becoming restrictive. In part, this hasled to the development of other technolo-gies, such as Java, Virtual Reality ModelingLanguage (VRML), and Extensible Mark-up Language (XML).See also Extensible Markup Language;Java; Secure HTTP; Virtual RealityModeling Language.Hypertext Transfer Protocol Abbrevi-ated HTTP. The command and control pro-tocol used to manage communicationsbetween a Web browser and a Web server.When you access a Web page, you see amixture of text, graphics, and links to otherdocuments or other Internet resources.HTTP is the mechanism that opens the re-lated document when you select a link, nomatter where that document is located.Hz See hertz.2461book Page 173 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 179. I2O174II2O See Intelligent Input/Output.IAB See Internet Architecture Board.IAC See Inter-ApplicationCommunication.IANA See Internet Assigned NumbersAuthority.IBM See International Business Ma-chines Corporation.IBM 3270 A general name for a family ofIBM system components—printers, termi-nals, and terminal cluster controllers—thatcan be used with a mainframe computer byan SNA (Systems Network Architecture)link.Software that emulates a 3270 terminal isavailable for all major operating systems.IBM cabling systems See Type 1-9cable.IBM Certified Advanced TechnicalExpert One of the many certificationsfrom IBM, available in many specializa-tions, including RS/6000 AIX.IBM Certified AIX User One of themany certifications from IBM. This one isavailable to the AIX user.IBM Certified Expert One of the manycertifications from IBM, available in arange of specializations, including OS/2Warp Server and OS/2 LAN Server.IBM Certified Specialist One of themany certifications from IBM, available ina range of specializations, including:IAIX System AdministrationIAIX SupportIAS/400 Associate System OperatorIAS/400 Professional System OperatorIAS/400 Associate System AdministratorIAS/400 Professional System AdministratorIOS/2 Warp Server AdministrationILAN Server 4 AdministrationIBM Certified Systems Expert One ofthe many certifications from IBM, availablein a range of specializations, includingOS/2 Warp and OS/2 Warp 4.IBM RS/6000 A set of seven or nine sep-arate 32-bit chips used in IBM’s line of re-duced instruction set computing (RISC)workstations.With as many as 7.4 million transistors, theRS/6000usesasuperscalardesignwithfourseparate 16KB data-cache units and an 8KBinstruction cache. The joint venture an-nounced between IBM, Apple, and Motor-ola in late 1991 specified the developmentof a single-chip version of the RS/6000 ar-chitecture called the PowerPC.IBM Suite for Windows NT Asoftwaresuite from IBM for Microsoft Windows NTthat includes five major modules:IIntel’s LANDesk Manager2461book Page 174 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 180. 175IEEE standardsILotus DominoIIBM’s DB2 Universal Database (UDB)IIBM’s eNetwork Communications ServerIIBM’s ADSTAR Distributed StorageManager (ADSM)The suite is available in both departmentand enterprise versions.IBM ThinkPad Aseriesofinnovativeandpopular notebook computers from IBM.The ThinkPad first introduced the touch-sensitive dual-button pointing stick (calleda TrackPoint), the pencil-eraser–like de-vice, found between the G, H, and B keys.It is now included on many portable com-puters and replaces the mouse.The top-of-the-line ThinkPad 770 runs a300MHz Pentium II processor, an 8.1GBhard disk, a 56K modem, a 14.1-inchSVGA screen with resolutions up to 1280 ×1024, and as much as 320MB of memory.IC See integrated circuit.ICA See Independent ComputingArchitecture.ICMP See Internet Control MessageProtocol.ICP See Internet Content Provider.Icon A general-purpose high-level pro-gramming language with a large number ofstring-processing functions, developed byRalph Griswold at the University of Arizo-na. Icon has a C-like syntax and is availableboth as a compiler and as an interpreter.icon In a graphical user interface, a smallscreenimagerepresentingaspecificelementthat the user can manipulate in some way,selected by moving a mouse or anotherpointing device.An icon can represent an application, adocument, embedded and linked objects, ahard disk drive, or several programs col-lected in a group.IDE See Integrated Drive Electronics.identity In Microsoft Outlook Express, afeature that allows you to create multipleaccounts so that you can keep business andpersonal e-mail associated with differentidentities.idle cell In Asynchronous TransferMode, a cell transmitted purely to keep net-work traffic at a specific level.See also Asynchronous Transfer Mode.IDS See Intrusion Detection System.IDT See Integrated Device Technology,Inc.IE See Internet Explorer.IEC See Interexchange Carrier.IEEE See Institute of Electrical and Elec-tronics Engineers.IEEE standards The Institute of Electri-cal and Electronics Engineers (IEEE), actingas a coordinating body, has established anumber of telecommunications standards,including Group 802 as follows:I802.1D An access-control standard forbridges linking 802.3, 802.4, and 802.5networks.I802.2 A standard that specifies the DataLink layer for use with 802.3, 802.4, and802.5 networks.2461book Page 175 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 181. IETF176I802.3 1Base5 A standard matching theAT&T StarLAN product with a 1Mbpsdata transfer rate and a maximum cable-segment length of 500 meters (1640 feet).I802.310Base2 AnimplementationoftheEthernet standard on thin Ethernet cablewith a data transfer rate of 10Mbps, and amaximum cable-segment length of 185meters (600 feet).I802.3 10Base-T A standard for Ether-net over unshielded twisted-pair wiring,the same wiring and RJ45 connectorsused with telephone systems. The stan-dard is based on a star topology, in whicheach node connects to a central wiringcenter, with a cable-length limitation of100 meters (325 feet).I802.3 10Broad36 A standard for long-distance Ethernet with a 10Mbps datarate and a maximum cable-segmentlength of 3600 meters (11,800 feet).I802.4 A standard for bus topology net-works that use token passing to controlaccess and network traffic, running at10Mbps. Not widely implemented.I802.5 A standard for ring networks thatuse token passing to control access andnetwork traffic, running at 4Mbps or16Mbps. It is used by IBM’s Token Ringnetwork.I802.6 An emerging standard for metro-politan area networks (MANs) transmit-ting voice, video, and data over twoparallel fiber-optic cables, using signalingrates of up to 155Mbps.I802.7 The Broadband Technical Advi-sory Committee provides advice onbroadband techniques to other IEEEsubcommittees.I802.8 The Fiber-Optic TechnicalAdvisory Committee provides advice onfiber-optic technology to other IEEEsubcommittees.I802.9 The Integrated Data and Voice(IDV) Networks group is currently work-ing to integrate data, voice, and video to802 LANs and ISDN. Now more com-monly referred to as Iso-Ethernet.I802.10 The Network Security Techni-cal Advisory Group is developing a stan-dard definition of a network securitymodel.I802.11 TheWirelessNetworkinggroupis developing standards for wirelessnetworks.I802.12 The Demand Priority group isworking on standards for the 100MbpsEthernet standard.I802.14 The Cable Modems group is de-fining standards for data transport overtraditional cable TV networks.You will also see many of these standardsreferred to by their ISO reference numbers.IEEE standards 802.1 through 802.11 arealso known as ISO standards 8802.1through 8802.11.For more information, see the entries onthe individual standards.IETF See Internet Engineering TaskForce.IFS See installable file system.IGMP See Internet Group ManagementProtocol.2461book Page 176 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 182. 177Incumbent Local Exchange CarrierIGP See Interior Gateway Protocol.IGRP See Interior Gateway RoutingProtocol.IIOP See Internet Inter-ORB Protocol.IKE Abbreviation for Internet KeyExchange.See ISAKMP/Oakley.ILEC See Incumbent Local ExchangeCarrier.IMA See Inverse Multiplexing over ATM.image map A graphical inline image ona Web page that contains more than onelink. Each region of the image map is linkedto a different Web resource; you can click apart of the image to retrieve the appropriateresource.See also inline image.imaging The process of capturing, stor-ing, cataloging, displaying, and printinggraphical information, as well as scanningpaper documents for archival storage.Network users can store and then retrieveimaged documents from large, centralizedimage-storage systems, using applicationssuch as Lotus Notes or other groupware.See also document management; high-capacity storage system; optical characterrecognition.IMAP See Internet Mail AccessProtocol.impedance An electrical property of acable that combines capacitance (the abilityto store an electrical charge), inductance(the ability to store energy in the form of amagnetic field), and resistance (the abilityto impede or resist the flow of electric cur-rent), measured in ohms.Impedance can be described as the apparentresistance to the flow of alternating currentat a given frequency. Mismatches in imped-ance along a cable cause distortions and re-flections. Each transmission protocol andnetwork topology specifies its own stan-dards for impedance.impersonation attack An attack inwhich a hostile computer system masquer-ades as a trusted computer.See also brute-force attack; dictionaryattack; social engineeringimplied security equivalence In Nov-ell Directory Services, when an object re-ceives the rights of the object’s parent, it issaid to be security equivalent. Also knownas container security equivalence. The In-herited Rights Filter does not affect this.See also explicit security equivalence; In-herited Rights Filter; Novell Directory Ser-vices; security equivalence.I-Mux See inverse multiplexing.incremental backup Abackupofaharddisk that consists of only those files createdor modified since the last backup.See also differential backup; full backup.Incumbent Local Exchange CarrierAbbreviated ILEC. A term coined from theTelecommunicationsActof1996todescribethe incumbent local telephone company,2461book Page 177 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 183. Independent Computing Architecture178providing local transmission and switchingservices.See also Competitive Local ExchangeCarrier.Independent Computing ArchitectureAbbreviated ICA. A presentation serviceprotocol developed by Citrix that transportsmouseclicks,keystrokes,andscreenupdatesbetween a thin client and the server. ICAworks with Microsoft Windows, Macin-tosh, and Unix clients and runs on top ofTCP/IP, IPX/SPX, and NetBIOS.See also thin client.Independent Software Vendor Ab-breviated ISV. A company that developsand sells computer software but is com-pletely independent of the makers of thehardware upon which the software runs.Industry Standard Architecture Ab-breviated ISA. The 16-bit bus design firstused in IBM’s PC/AT computer in 1984.ISA has a bus speed of 8MHz and a maxi-mum throughput of 8MBps. EISA (Extend-ed Industry Standard Architecture) is a 32-bit extension to this bus.INETCFG A Novell NetWare 4 NLMused to set up and configure AppleTalk, In-ternet Protocol (IP) and InternetworkingPacket eXchange (IPX) protocols on theserver.infection The presence of a virus or aTrojan Horse within a computer system;the virus may be active in memory orpresent on the hard disk.The infection may remain hidden from theuser for a considerable length of time. Someviruses are triggered by particular dates,others by specific events on the system.See also antivirus program; boot sector vi-rus; file-infecting virus; inoculate; macrovirus; multipart virus; polymorphic virus;stealth virus; Trojan Horse; vaccine; virus.information node Abbreviated i-node,sometimes written inode, pronounced“eye-node.” In Unix, a data structure ondisk that describes a file.Each directory entry associates a filenamewith an i-node; although a single file mayhave several filenames, one for each link , afile has only one i-node. Within a filesys-tem, the number of i-nodes, and thereforethe number of files, is defined when the sys-tem is first initialized.An i-node contains all the information Unixneeds to be able to access the file, includingthe file’s length, the times that the file waslast accessed or modified, owner and groupID information, access permissions, thenumber of links to the file, and the disk ad-dress of the data blocks that contain the fileitself.See also i-node table.information warehouse A centralrepository containing a company’s currentand historical data in a form that can beaccessed quickly and easily by users to aidin their business decision making. IBM hasa large number of products for buildingfully automated enterprise-wide datawarehouses.Informix-4GL Certified ProfessionalA professional certification from InformixSoftware aimed at developers proficient in2461book Page 178 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 184. 179initializecreating custom database applications us-ing Informix-4GL.Informix Software, Inc. A major sup-plier of object-oriented and relational data-base products, based in Menlo Park,California.For more information on Informix Soft-ware, Inc., see Data Association Abbreviat-ed IrDA. A trade association of more than150 computer and telecommunicationshardware and software suppliers, includingHewlett-Packard, Apple Computer, AST,Compaq, Dell, IBM, Intel, Motorola, Nov-ell, and others.IrDA is concerned with defining stan-dards for products that use wirelesscommunications.For more information on IrDA, see transmission A method ofwireless transmission that uses part of theinfrared spectrum to transmit and receivesignals.Infrared transmissions take advantage of afrequency range just below that of visiblelight, and they usually require a line-of-sight connection between transmitter andreceiver.Infrared transmission can be used to senddocuments from portable computers toprinters, to transmit data between portablecomputers, to exchange information be-tween computers and cellular telephonesand faxes, and to connect to home entertain-ment systems. Almost every manufacturerof portable devices is implementing infraredcommunications at some level.See also Infrared Data Association; mobilecomputing; wireless communications.inherited rights Rights (in Novell Net-Ware) or permissions (in Microsoft Win-dows 2000) received by an object from itsparentobject.InNovellNetWare,inheritedrights can be blocked by the InheritedRights Filter or by an explicit assignment.See also Inherited Rights Filter.Inherited Rights Filter AbbreviatedIRF. In Novell Directory Services (NDS),the mechanism that controls the rights atrustee can inherit from parent directoriesor container objects.Inheritance allows an assignment applied atone point to apply to everything below thatpoint in the file and directory structure. TheIRF for any file, directory, or object is a partof NetWare’s access control information.In NetWare 3, the IRF was known as the In-herited Rights Mask and applied only to thefile system.See also Inherited Rights Mask; NETAD-MIN; trustee; trustee assignment.Inherited Rights Mask AbbreviatedIRM. In NetWare 3, the mechanism thatcontrols the rights a trustee can inherit. Bydefault, IRM allows all rights to be inherit-ed. Both files and directories have individ-ual IRM controls.See also Inherited Rights Filter; trustee;trustee assignment.initialize 1. To start up a computer.2461book Page 179 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 185. inline image1802. In the Macintosh, the process of prepar-ing a new, blank floppy or hard disk for use.Initializing completely obliterates any in-formation previously stored on the disk.3. To assign a beginning value to a variable.See also formatting.inline image On a Web page, an imagedisplayed along with accompanying text.The process of placing the image on thepage is known as inlining.inoculate To protect a file against attackfrom a virus by recording characteristic in-formationaboutitandthenmonitoringanychanges.See also antivirus program; boot sector vi-rus; file-infecting virus; infection; macro vi-rus; multipart virus; polymorphic virus;stealth virus; Trojan Horse; vaccine; virus.i-node See information node.i-node table In Unix, a list of all thei-nodes in a filesystem. Within the i-nodetable, each i-node is known by a number—the i-number, or index number. If a file isdefined by i-node #300, it is said to have ani-number of 300.See also information migration In Novell NetWare,a method of upgrading an existing Net-Ware server to NetWare 4, which includesconverting the file system and updating thenetwork operating system.See also across-the-wire migration.Inprise Corporation Originally knownas Borland International, the companychanged its name in 1988. Well known forits dBASE database products, the companyalso markets Delphi Client/Server Suite, avisual rapid applications development envi-ronment, and JBuilder, a set of Java pro-gramming language development tools.For more information on Inprise Corpora-tion, see Abbreviated I/O. Thetransfer of data between the computer andits peripheral devices, disk drives, termi-nals, and printers.input/output bound Abbreviated I/Obound. A condition in which the speed ofoperation of the input/output port limitsthespeedofprogramexecution.Gettingthedata into and out of the computer is moretime-consuming than actually processingthat same data.See also computation bound.INSTALL A Novell NetWare server con-sole NetWare Loadable Module (NLM)used for managing, maintaining, and up-dating NetWare servers. INSTALL can beused for the following tasks:ICreating, deleting, and managing hard-disk partitions and NetWare volumes onthe serverIInstalling NetWare and other additionalproducts and updating the license or reg-istration diskIAdding, removing, checking, and unmir-roring hard disksIChanging server startup and configura-tion files2461book Page 180 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 186. 181Integrated Device Technology, Inc.install To configure and prepare hard-ware or software for operation.Many application packages have their owninstallation programs, which copy all therequired files from the original distributiondisks into appropriate directories on yourhard disk and then help to configure theprogram to your own operating require-ments. Microsoft Windows programs areinstalled by a program called Setup.installable file system AbbreviatedIFS. A file system that is loaded dynamicallyby the operating system when it is needed.Different file systems can be installed tosupport specific needs, in just the same wayas device drivers are loaded to support spe-cific hardware.installation program A program whosesole function is to install (and sometimesconfigure) another program.The program guides the user through whatmight otherwise be a rather complex set ofchoices, copying the correct files into theright directories, decompressing them ifnecessary, and asking for the next diskwhen appropriate. An installation programmay also ask for a person’s name and acompany name so that the startup screencan be customized. Microsoft Windowsprograms are installed by a program calledSetup.Installer service In Microsoft Windows2000, a service that manages all aspects ofapplication installation, removal, and theseparate configuration of components oflarge packages such as Office 2000.Institute of Electrical and ElectronicsEngineers Abbreviated IEEE, pro-nounced “eye-triple-ee.” A membership or-ganization, founded in 1963, includingengineers, students, and scientists. IEEEalso acts as a coordinating body for com-puting and communications standards.For more information in IEEE, also IEEE standards.instruction set The set of machine-lan-guage instructions that a processor recog-nizes and can execute.An instruction set for reduced instructionset computing (RISC) may only contain afew instructions; a computer that usescomplex instruction set computing (CISC)may be able to recognize several hundredinstructions.INT 14 See Interrupt 14.integrated circuit Abbreviated IC, alsoknown as a chip. A small semiconductorcircuit that contains many electroniccomponents.Integrated Device Technology, Inc.Abbreviated IDT. An established manufac-turer of SRAM, specialty memory, and em-bedded microprocessors, who has recentlymoved into producing clones of Intel micro-processors. IDT’s first WinChip, originallyknown as the C6, shipped in limited quan-tities in 1997 and 1998, and the companyrecently announced the WinChip 2 andWinChip 2+.For more information on Integrated DeviceTechnology, see Page 181 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 187. Integrated Drive Electronics182Integrated Drive Electronics Abbrevi-ated IDE. A popular hard-disk interfacestandard, used for disks in the range of40MB to 1.2GB, requiring medium to fastdata-transfer rates. The electronic controlcircuitry is located on the drive itself, thuseliminating the need for a separate hard-disk controller card.See also Enhanced Small Device Interface;Small Computer System Interface; ST506Interface.Integrated On-Demand NetworkAbbreviated ION. A new high-capacityresidential and business service fromSprint that allows customers to simulta-neously make a phone call, send/receive afax, and access the Internet using a singleconnection.The service is based on a mixture of broad-band technology, such as AsynchronousTransfer Mode (ATM) and Digital Sub-scriber Line (DSL). Deployment of the net-work is based on a partnership with threeother companies—Cisco Systems, Bellcore,and Radio Shack.See also Asynchronous Transfer Mode;Digital Subscriber Line.Integrated Services Architecture Ab-breviated ISA. A proposed extension to theInternet standards that would provide inte-grated services in support of real-time ap-plications over the Internet.Using current standards, real-time applica-tions do not work well over the Internetbecause of variable and unpredictablequeuing delays and other losses. To solvethis problem, ISA suggests that routers beable to reserve resources for specific datastreams called flows. A flow might be videodata from a source to a destination or froma source to multiple destinations.See also IP over ATM; IP switching; qualityof service.Integrated Services Digital NetworkAbbreviated ISDN. A standard for a world-wide digital communications network orig-inally designed to replace all current systemswith a completely digital, synchronous, full-duplex transmission system.Computers and other devices connect toISDN via simple, standardized interfaces.They can transmit voice, video, and data,all on the same line.See also Basic Rate ISDN; Broadband Inte-grated Services Digital Network; PrimaryRate ISDN.integrated software Application soft-ware that combines the functions of severalmajor applications, such as a spreadsheet, adatabase, a word processor, and a commu-nications program, into a single package.Microsoft Works is an example of integrat-ed software.Integrated software provides a consistentuser interface in all the modules and allowsthe user to transfer data from one part ofthe system to another quickly and easily. Itis also usually inexpensive. Unfortunately,integrated software packages do not typi-callyofferallthecomplexfeaturesavailablewith their stand-alone counterparts.See also software suite.2461book Page 182 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 188. 183Intel CorporationINTEGRATED SERVICES DIGITAL NETWORKIntegrated-Private Network-to-Network Interface Abbreviated I-PNNI.A routing protocol based on the Asynchro-nousTransferMode(ATM)Forum’sPrivateNetwork-to-Network Interface (PNNI)standard that allows ATM switches tocommunicate.See also Private Network-to-NetworkInterface.Intel Corporation The world’s largestmanufacturerofmicroprocessors,supplyingthe processors used in more than 80 percentof the world’s personal computers.Intel has developed a wide range of pro-cessors and board-level products that areused in applications as varied as personalcomputers, automobiles, robots, andsupercomputers, as well as the multibusarchitecture that is used in many industri-al and proprietary applications. Intel alsomanufactures modems, fax modems,memory chips, flash memory products,and other peripheral devices. The nameIntel is a contraction of IntegratedElectronics.2461book Page 183 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 189. Intelligent Input/Output184For more information on Intel Corpora-tion, see Input/Output AbbreviatedI2O; pronounced “eye-two-oh.” A specifi-cation from Intel Corporation that dividesthe traditional device driver into two parts;IThe part concerned with managing thedeviceIThe part concerned with interfacing to theoperating systemBy making this distinction, that part of thedriver concerned with managing the devicenow becomes portable across operatingsystems.I2O is also designed to work with intelligentinput/output subsystems, with support formessage passing between multiple indepen-dent processors, so that the host system canberelievedofalltheinterrupt-intensivetasksassociated with servicing device drivers.Several operating system vendors, includ-ing SCO, Microsoft, and Novell, have an-nounced support for I2O in futureproducts.intelligent hub See smart hub.intelligent terminal A terminal connect-ed to a large computer, often a mainframe,thathassomeleveloflocalcomputingpowerand can perform certain operations indepen-dently from the remote computer, but doesnot usually have any local disk-storagecapacity.See also dumb terminal.Interactive Unix A version of Unix fromSun Microsystems based on AT&T’s Sys-tem V Release 3.2 kernel.See also Solaris.Inter-Application CommunicationAbbreviated IAC. In the Macintosh operat-ing system, a feature of the System softwarethat allows independent applications toshare and exchange information. IAC takestwo main forms:IPublish-and-subscribe, which allows us-ers to create documents made of compo-nents created by multiple applications.IApple events, which let one applicationcontrol another. For example, two pro-grams can share common data, and oneprogram can request that the other per-form some action.IAC is often referred to as program linkingin the System manuals.Interexchange Carrier AbbreviatedIXC; sometimes abbreviated IEC. A termcoined from the Telecommunications Actof 1996 to describe voice and data long-distance telephone companies, includingAT&T, MCI, Sprint, and Worldcom.See also Competitive Local Exchange Car-rier; Incumbent Local Exchange Carrier;Local Exchange Carrier.interface Thepointatwhichaconnectionis made between two hardware devices, be-tween a user and a program or operating sys-tem, or between two applications.In hardware, an interface describes thelogical and physical connections, as inRS-232-C, and is often considered synon-ymous with the term port.A user interface consists of the means bywhich a program communicates with the us-2461book Page 184 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 190. 185International Business Machines Corporationer, including a command line, menus, dialogboxes, online help systems, and so on. Userinterfaces can be classified as character-based, menu-driven, or graphical.Software interfaces are application pro-gramming interfaces (APIs) and consist ofthe codes and messages used by programsto communicate behind the scenes.See also graphical user interface.interface standard Any standard wayof connecting two devices or elements thathave different functions.Personal computers use many different in-terface standards. These include SmallComputer System Interface (SCSI), Inte-grated Drive Electronics (IDE), and the En-hanced Small Device Interface (ESDI) forhard disks; RS-232-C and the Centronicsparallel interface for serial devices and par-allel printers; and the OSI Reference Modelfor LAN communications over a network.Interior Gateway Protocol Abbreviat-ed IGP. The protocol used on the Internetto exchange routing information betweenrouters within the same domain.See also Border Gateway Protocol; Exter-nal Gateway Protocol.Interior Gateway Routing ProtocolAbbreviated IGRP. A distance-vector rout-ing protocol from Cisco Systems for use inlarge heterogeneous networks.See also heterogeneous network.interleaved memory A method ofspeeding up access by dividing dynamicRAM (DRAM) into two (or more) separatebanks.DRAM requires that its contents be updat-ed at least every thousandth of a second,and while this update is taking place, it can-not be read by the processor. Interleavedmemory divides available memory intobanks so that the processor can read fromone bank while the other is cycling and sodoes not have to wait. Because interleavedmemory does not require special hardware,it is one of the most cost-effective ways ofspeeding up system operation.See also wait state.internal command Any operating sys-tem command that is not a separate pro-gram and is always available to the user. InMS-DOS, DIR, COPY, and TYPE are ex-amples of internal commands.See also external command.internal modem A modem that plugsinto the expansion bus of a personal com-puter or into the PCMCIA connector of alaptop computer.See also external modem.internal security Security measures tak-en to prevent unauthorized computer ac-cess from within an organization.See also Intrusion Detection System.International Business MachinesCorporation Abbreviated IBM, alsoknown as “Big Blue.” Known originally forits huge range of mainframe computers,IBM introduced the IBM PC, which quicklyemerged as an industry standard. Since itsintroduction in 1981, the PC has seen manychanges, and an enormous number of com-panies worldwide now manufacture or2461book Page 185 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 191. International Organization for Standardization186market hardware, software, and peripheraldevices for IBM-compatible computers.IBM also has a huge research effort, ownsthousands of patents, and has introducedmany innovative products, including thesmall, touch-sensitive TrackPoint, whichreplaces the mouse on many portable com-puters, a 1000MHz chip, and a 3.5-inchhard disk drive capable of storing up to17GB of information.For more information on IBM, also Advanced Program-to-ProgramCommunications; Advanced Peer-to-Peer Networking; Advanced InteractiveExecutive; AS/400; Systems NetworkArchitecture.International Organization for Stan-dardization Sometimes mistakenly re-ferred to as the International StandardsOrganization, and commonly referred to asISO, which is not an abbreviation but a der-ivation of the Greek word isos, whichmeans equal and which is a term that wasadopted by the International Organizationfor Standardization. An international stan-dards-making body, based in Geneva, withrepresentatives from more than 100 coun-tries. The ISO establishes global standardsfor communications and information ex-change. ANSI is the U.S. member of theISO.The seven-layer OSI Reference Model forcomputer-to-computer communications isone of the ISO’s most widely accepted rec-ommendations in the area of networking.For more information on ISO, also OSI Reference Model.International TelecommunicationUnion Abbreviated ITU. The U.N. um-brella organization that develops and stan-dardizes telecommunications worldwide.The ITU also contains the CCITT, the In-ternational Frequency Registration Board(IFRB), and the Consultative Committeeon International Radio (CCIR). In popularusage, CCITT standards are being referredto as ITU standards.For more information on ITU, The world’s largest computernetwork, consisting of millions of comput-ers supporting tens of millions of users inhundreds of countries. The Internet isgrowing at such a phenomenal rate that anysize estimates are quickly out of date.The Internet was originally established tomeet the research needs of the U.S. defenseindustry, but it has grown into a huge glo-bal network serving universities, academicresearchers, commercial interests, govern-ment agencies, and private individuals,both in the United States and overseas.The Internet uses TCP/IP protocols, and In-ternet computers run many different oper-ating systems, including VMS, MicrosoftWindows 2000, and many variations ofUnix.No government agency, single person, orcorporate entity controls the Internet; thereis no Internet Corporation working behindthe scenes. All decisions on methods andstandardsaremadebycommitteesbasedoninput from users.2461book Page 186 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 192. 187Internet abbreviationsInternet use falls into several major areas,including:IE-mail Electronic mail. Well over 80percent of the people who use the Internetregularly use it for e-mail. You can sende-mail to recipients in more than 150countries, as well as to subscribers of com-mercial online services, such as AmericaOnline, CompuServe, Delphi, Genie, andProdigy.IIRC chat A service that connects largenumbers of users in real-time groupdiscussions.IMailing lists Private discussion groupsaccessed by e-mail.IUsenet newsgroups Larger public dis-cussion groups that focus on a specificsubject. Posts and threads in newsgroupsare accessed using a newsreader.IWorld Wide Web Hypertext-based sys-tem for finding and accessing Internet re-sources; the World Wide Web is one of thefastest growing and most exciting of allInternet applications.Other Internet applications such as Go-pher, FTP and anonymous ftp, and Telnethave either been overshadowed by thegrowth of the World Wide Web or haveseen their function absorbed into the pop-ular Web browsers.The sheer volume of information availablethrough the Internet is staggering; however,because the Internet is a casual grouping ofmany networks, there is often no easy wayto determine the location of specific infor-mation. This has led to the emergence ofseveralprominentportalsitesandanumberof popular search engines.Internet access can be via a permanent net-work connection or by dial-up through oneof the many Internet Service Providers (ISP).See also Internet address; Internet Archi-tecture Board; Internet Assigned NumbersAuthority; Internet Engineering TaskForce; Internet Research Task Force; Inter-net Society; portal; Request for Comment;search engine; Usenet; World Wide Web;World Wide Web Consortium.internet See internetwork.Internet abbreviations Like any cul-ture, the Internet world has developed awhole language of abbreviations, acro-nyms, and slang expressions. The followinglist describes some of the common termsyou are likely to encounter in Usenet news-groups or in your e-mail.See also emoticon; smiley.Abbreviation DescriptionaTdHvAaNnKcSe Thanks in advanceAWTTW A word to the wiseBRB Be right back2461book Page 187 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 193. Internet abbreviations188BTW By the wayCU See youFAQ Frequently asked questionFAQL Frequently asked question listFOAF Friend of a friendF2F Face to faceFWIW For what it’s worthGR&D Grinning, running, and duckingIMHO In my (sometimes not very) humble opinionIWBNI It would be nice ifIYFEG Insert your favorite ethnic groupLOL Laughing out loudMEGO My eyes glaze overMOTAS Member of the appropriate sexMOTOS Member of the opposite sexMOSS Member of the same sexOb- Obligatory, as in ob-jokeOTOH On the other handPD Public domainAbbreviation Description2461book Page 188 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 194. 189Internet Architecture BoardInternet address A location on the In-ternet. An Internet address takes the, in whichsomeone isa user’s name or part of a user’s name, @abcis the network computer of the user, anddef is the name of the host organization.The last three letters denote the kind of in-stitution the user belongs to:edu for educationalcom for commercialgov for governmentmil for the militaryorg for non-profit organizationsnet for Internet administrativeorganizationsSee also bang path; IP address.Internet Architecture Board Abbrevi-ated IAB. A technical advisory group of theInternet Society (ISOC). The IAB managesthe editing and publication of Request forComments (RFCs), serves as an appealsboard, and provides other services to theISOC.For more information on the IAB, Pain in the assPMFJI Pardon me for jumping inRL Real lifeROTFL Rolling on the floor laughingRTFM Read the (expletive deleted) manualSO Significant otherTIA Thanks in advanceTTFN Ta ta for nowWRT With respect toYMMV Your mileage may vary$0.02 My two cents worthAbbreviation Description2461book Page 189 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 195. Internet Assigned Numbers Authority190Internet Assigned NumbersAuthority Abbreviated IANA. A centralclearinghouse for the assignment and coor-dination of Internet protocol parameters,such as Internet addresses, protocol vari-ables and numbers, and domain names.For more information on the IANA, Connection Sharing In Mi-crosoft Windows 98 and Windows 2000, amechanism that allows networked com-puters to share a single connection to theInternet.Internet Connection Sharing works withany kind of Internet connection, includingmodems, Integrated Services Digital Net-work (ISDN), cable modem, or Digital Sub-scriber Line (DSL).Internet Content Provider Abbreviat-ed ICP. A company that will design and de-liver content for your Web site.See also Internet Service Provider.Internet Control Message ProtocolAbbreviated ICMP. An error-reporting pro-tocol that works with Internet Protocol (IP)and provides the functions used for network-layer management and control.Routers send ICMP messages to respond toundeliverabledatagramsbyplacinganICMPmessage in an IP datagram and then sendingthe datagram back to the original source.ICMP is also used by the Ping command.See also Ping.Internet Engineering Task Force Ab-breviated IETF. Provides technical and de-velopment services for the Internet andcreates, tests, and implements Internet stan-dards that are then approved and publishedby the Internet Society (ISOC). The techni-cal work is done within the IETF workinggroups.For more information on IETF, Explorer Abbreviated IE. InMicrosoft Windows, a Web browser usedto display Internet resources.See also security zone.Internet file types The Internet offersmany opportunities for downloading filesfrom a huge number of Internet hosts.These files may have been generated on dif-ferent computer systems, so before youspend time downloading a file, it is impor-tant to understand the type of file you aredealing with. Table I.1 lists many of thecommon file types you may encounter.TABLE I.1 INTERNET FILE TYPESFilename Extension Descriptiontar A tape archive created by the tar utility.Z A file created by the compress utility. You must use uncompressto restore the file before you can use it.2461book Page 190 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 196. 191Internet file typestar.z A compressed tape archive file.z A file created by the pack utility. You must use unpack to restorethe file before you can use A file created by PKZIP or WinZip. You must unzip the file beforeyou can use it.gz A file created by the GNU gzip utility. You must decompress thefile before you can use it.hqx A compressed Macintosh file.sit A Macintosh file compressed by StuffIt.tif/tiff A graphics file in TIF format.gif A graphics file in GIF format.htm/html A Web page in HyperText Markup Language.jpg/jpeg A graphics file in JPEG format.mpg/mpeg A video file in MPEG format.txt A text file.1 An nroff source A PostScript file ready for printing.uue A uuencoded file. You must use uudecode before you can usethe file.uue.z A compressed uuencoded file.shar A Usenet newsgroup archive file created by the shar utility.shar.z A compressed shar file.TABLE I.1 INTERNET FILE TYPES (CONTINUED)2461book Page 191 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 197. Internet Group Management Protocol192Internet Group Management Pro-tocol Abbreviated IGMP. An Internetprotocol used in multicasting.IGMP allows hosts to add or removethemselves from a multicast group. A mul-ticast group is a collection of computers re-ceiving packets from a host that is trans-mitting multicast packets with IP Class Daddresses. Group members can join thegroup and leave the group; when there areno more members, the group simply ceasesto exist.See also Class D network; IP Multicast;multicasting.Internet Inter-ORB Protocol Abbrevi-ated IIOP. That part of the Common ObjectRequest Broker Architecture (CORBA)that allows CORBA-based interaction overTCP/IP networks (including the Internet)by replacing Hypertext Transfer Protocol(HTTP).See also Common Object Request BrokerArchitecture.Internet Key Exchange See ISAKMP/Oakley.Internet Mail Access Protocol Abbre-viated IMAP. A protocol that defines howusers can access and store incoming e-mailmessages.Internet mail servers use Simple MailTransfer Protocol (SMTP) to move e-mailfrom one server to another and then useeither IMAP or Post Office Protocol (POP)to manage the e-mail and store messages inthe appropriate mailboxes.IMAP allows users to download mail selec-tively, to look at a message header, todownload only part of a message, to storemessages on the server in a hierarchicalstructure, and to link to documents andUsenet newsgroups. IMAP also has strongauthentication features and supports Ker-beros. Search commands are also availableso that users can locate messages based ontheir subject or header or based on content .See also Kerberos; Post Office Protocol;Simple Mail Transfer ProtocolInternet Network File System Abbre-viated Internet NFS. A TCP/IP-based pro-tocol from Sun Microsystems used forsharing and accessing files remotely overthe Internet.See also Network File System.Internet Network Information CenterAbbreviated InterNIC. A cooperative ven-ture between AT&T, the National ScienceFoundation, and Network Solutions, Inc.,that provides domain name registration andassigns IP addresses for use on the Internet.For more information on InterNIC, NFS See Internet Network FileSystem.Internet Protocol Abbreviated IP, IPversion 4, and IPv4. The session-layer pro-tocol that regulates packet forwarding bytracking addresses, routing outgoing mes-sages, and recognizing incoming messagesin TCP/IP networks and the Internet.2461book Page 192 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 198. 193Internet Relay ChatTheIPpacketheadercontainsthefollowingfields:IVersion Version number of the protocol.IIHL (Internet header length) Length ofthe header information. The header lengthcan vary; the default header is five 32-bitwords, and a sixth word is optional.ITOS (Type of Service) Various levels ortypes of service.ITotal length Length of the datagram inbytes, which can be a minimum of 576bytes to a maximum of 65,535 bytes.IIdentification Information that the re-ceiving system can use to reassemble frag-mented datagrams.IFlags Thefirstflagbit(DF)specifiesthatthe datagram should not be fragmentedand must therefore travel over networksthat can handle the size without fragment-ing it. The second flag bit (MF) indicateswhether this is the last fragment.IFragment Offset An indication of wherethis datagram belongs in the set of frag-ments; is used during reassembly.ITime-to-Live (TTL) Originally, thetime in seconds that the datagram couldbe in transit; if this time was exceeded,the datagram was considered lost. Nowinterpreted as a hop count and usually setto the default value 32 (for 32 hops), thisvalue is decremented by each routerthrough which the packet passes. Once itreaches zero, the datagram is discarded.IProtocol Identifies the transport-layerprocess intended to receive the datagram.A value of 6 indicates Transmission Con-trol Protocol (TCP), and a value of 17 in-dicates User Datagram Protocol (UDP).IHeader checksum Checksum for theheader.ISource address IP address of the sender.IDestination address IP address of therecipient.IOptions/padding Optionalinformationand padding.See also IP multicast; IPv6; TransmissionControl Protocol; Transmission ControlProtocol/Internet Protocol.Internet Relay Chat Abbreviated IRC.An Internet client/server application that al-lows large groups of people to communi-cate interactively; developed by JarkkoOikarinen in Finland.Specificchannelsaredevotedtoaparticularsubject, from the sacred to the profane, andchannels come and go regularly as interestlevels change. Each channel has its ownname, usually prefaced by the pound sign(#), as in #hottub.When you join a channel, you can see whatothers have already typed; when you type aline and press Enter, everyone else sees yourtext. Most, but not all, of the conversationsare in English. If someone asks you for apassword during an IRC session, don’t betempted to give it; someone is trying to trickyou into divulging important informationabout your system.See also listserver; mailing list; news-group; Usenet.2461book Page 193 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 199. Internet Research Task Force194INTERNET PROTOCOL FIELDSInternet Research Task Force Abbre-viated IRTF. An Internet organization thatcreates long- and short-term researchgroups concentrating on protocols, archi-tecture, and technology issues.For more information on IRTF, Service Provider AbbreviatedISP.Acompanythatprovidescommercialorresidential customers access to the Internetvia dedicated or dial-up connections. An ISPwill normally have several servers and ahigh-speed connection to an Internet back-bone. Some ISPs also offer Web site hostingservices and free e-mail to their subscribers.See also Internet Content ProviderInternet Society Abbreviated ISOC. Aninternational organization that promotescooperation and coordination for the Inter-net, Internet applications, and internet-working technologies.ISOC also coordinates the activities ofmany other Internet groups, including theInternet Architecture Board (IAB), the In-ternet Engineering Task Force (IETF), theInternet Assigned Numbers Authority(IANA), and the Internet Research TaskForce (IRTF).For more information on ISOC, Abbreviated internet.Two or more networks using differentnetworking protocols, connected by meansof a router. Users on an internetwork canaccess the resources of all connectednetworks.Internetwork Operating System SeeInternetworking Operating System.2461book Page 194 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 200. 195Internetwork Packet eXchangeInternetworking Operating SystemAbbreviated IOS; sometimes referred to asInternetwork Operating System Propri-etary operating system software that runson the Cisco family of routers.IOS is stored in flash memory or in RAM inthe router and supports remote access andprotocol translation services, with connec-tivity provided by terminals, modems, com-puters, printers, or workstations. LANterminal support includes TransmissionControl Protocol/Internet Protocol (TCP/IP) for telnet and rlogin connections to IPhosts,tn3270forconnectionstoIBMhosts,and LAT (Local Area Transport) for con-nections to DEC hosts.For WANs, IOS supports connections overa dial-up line supporting AppleTalk Re-mote Access, Serial Line Internet protocol(SLIP), Compressed SLIP (CSLIP), andPoint-to-Point protocol (PPP) and supportsasynchronous terminal connections usingterminal emulation software providing tel-net, rlogin, or IBM 3270 protocols.IOS also supports Simple Network Man-agement Protocol (SNMP), Common Man-agement Information Protocol/CommonManagement Information Services (CMIP/CMIS) and IBM’s Network ManagementVector Transport (NMVP) network man-agement systems.You can configure IOS to control whichnetworking protocols are routed, whichprotocols are used to do the actual routing,which interfaces on the router are used forspecific routed protocols, and which pro-cesses will execute on the router.Internetwork Packet eXchange Ab-breviated IPX. Part of Novell NetWare’snative protocol stack, used to transfer databetween the server and workstations on thenetwork. IPX packets are encapsulated andcarried by the packets used in Ethernet andthe frames used in Token Ring networks.IPX packets consist of a 30-byte headerwhich includes the network, node, andsocket addresses for the source and the des-tination, followed by the data area, whichcan be from 30 bytes (only the header) to65,535 bytes in length. Most networks im-pose a more realistic maximum packet sizeof about 1500 bytes.The IPX packet header contains the follow-ing fields:IChecksum For data integrity checking..IPacket length Length of the packet inbytesITransport control Number of routers apacket can cross before being discardedIPacket type The service that created thepacketIDestination network Network addressof the destination networkIDestination node Media access control(MAC) address of the destination nodeIDestination socket Address of the pro-cess running on the destination nodeISource network Network address of thesource networkISource node Media access control(MAC) address of the source nodeISource socket Address of the processrunning on the source nodeSee also Sequenced Packet Exchange.2461book Page 195 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 201. Internetwork Packet Exchange Open Data-Link Interface196Internetwork Packet Exchange OpenData-Link Interface AbbreviatedIPXODI. In Novell NetWare, the clientsoftware that accepts data from the DOSRequester, adds header and address infor-mation to each data packet, and transmitsthe data packet as a datagram.InterNIC See Internet Network Informa-tion Center.interoperability The ability to run appli-cation programs from different vendorsacross LANs, WANs, and MANs, givingusers access to data and applications acrossheterogeneous networks. A network userneed not know anything about the operat-ing system or the configuration of the net-work hardware to access data from the fileserver.Interoperabilityisboostedbytheincreasingavailability of products that conform toopen standards rather than to specific pro-prietary protocols. The products work inaccordance with national and internation-ally accepted standards.interpreter A programming languagetranslator that converts high-level programsource code into machine language state-ments one line at a time.Unlike a compiler, which must translate thewhole program before execution can begin,an interpreter translates and then executeseach line one at a time; this usually meansthat an interpreted program runs moreslowly than a compiled program.Java is an interpreted language, BASIC wasoften interpreted, although recent releaseshave used a compiler instead, and C andC++ are always compiled.See also compiler; Java; just-in-timecompiler.interprocess communication Abbre-viated IPC. A term that describes all themethods used to pass information betweentwo programs running on the same com-puter in a multitasking operating system orbetween two programs running on a net-work, including pipes, shared memory,message queues, sockets, semaphores, andObject Linking and Embedding (OLE).See also Inter-Application Communication.Interrupt 14 Abbreviated INT 14. ThePC interrupt used to reroute messages fromthe serial port to the network interface card(NIC); used by some terminal-emulationprograms.interrupt A signal to the processor gen-erated by a device under its control, such asthe system clock, that interrupts normalprocessing.An interrupt indicates that an event requir-ing the processor’s attention has occurred,causing the processor to suspend and saveits current activity and then branch to an in-terrupt service routine (ISR).In the PC, interrupts are often divided intothree classes:IInternal hardwareIExternal hardwareISoftware2461book Page 196 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 202. 197Intrusion Detection SystemThe Intel family of processors supports 256prioritized interrupts, of which the first 64are reserved for use by the system hardwareor by the operating system.See also interrupt request.interrupt controller A chip used to pro-cess and prioritize hardware interrupts. Inthe PC, a programmable interrupt control-ler responds to each hardware interrupt, as-signs a priority, and forwards it to the mainprocessor.See also interrupt request.interrupt handler Special software lo-cated in the operating-system kernel thatmanages and processes system interrupts.Also known as an interrupt service routine(ISR).When an interrupt occurs, the processorsuspends and saves its current activity andthen branches to the interrupt handler. Thisroutine processes the interrupt, whether itwas generated by the system clock, a key-stroke, or a mouse click. When the ISR iscomplete, it returns control to the suspend-ed process.Each type of interrupt is processed by itsown specific interrupt handler. A table,called the interrupt vector table, maintainsa list of addresses for these specific interrupthandlers.See also hooked vector.interrupt request Abbreviated IRQ.Hardware lines that carry a signal from adevice to the processor.A hardware interrupt signals that an eventhastakenplacethatrequirestheprocessor’sattention. The interrupt may come from thekeyboard, the network interface card(NIC), or the system’s disk drives.See also interrupt controller.interrupt service routine See inter-rupt handler.interrupt vector table A list of addresses,maintained by the operating-system kernel,for specific software routines known as inter-rupt handlers.See also interrupt handler.intranet A private corporate networkthat uses Internet software and TCP/IP net-working protocol standards.Many companies use intranets for tasks assimpleasdistributingacompanynewsletterand for tasks as complex as posting and up-dating technical support bulletins to servicepersonnel worldwide. An intranet does notalways include a permanent connection tothe Internet.See also extranet; Internet; internet.intruder An unauthorized user of a com-puter system, usually a person with mali-cious intent.See also cracker; firewall; hacker; IntrusionDetection System.Intrusion Detection System Abbrevi-ated IDS. A software package designed todetect specific actions on a network that aretypical of an intruder or that might indicatean act of corporate espionage.An IDS package monitors the network orthe server for specific “attack signatures”that might indicate an active intruder is2461book Page 197 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 203. inverse multiplexing198attempting to gain access to the network;such actions are carefully documented bythe system.Specific actions, such as opening or renam-ing certain important files, opening specificapplications, downloading large amounts ofdata from key documents, or sending classi-fied documents out as e-mail attachments,are also monitored by the IDS software.See also firewall.inverse multiplexing Abbreviated I-Mux. In communications, a technique thatsplits a high-speed data stream into two ormore parts for transmission over multiplelower-speed channels. Once at the receivingend of the circuit, the data streams are com-bined into a single stream.Inverse multiplexing provides bandwidth ondemand, to avoid the high costs associatedwith a leased line that may not be fully uti-lized at all times and to take advantage oflow-cost low-speed lines.See also multiplexing.Inverse Multiplexing over ATM Ab-breviated IMA. A specification defined bythe Asynchronous Transfer Mode (ATM)Forum that defines a method of inversemultiplexing ATM over two or more T1circuits.See also Asynchronous Transfer Mode;inverse multiplexing.inverted backbone A network architec-ture in which the wiring hub and routers be-come the center of the network; all thenetwork segments attach to this hub.See also backbone.INVERSE MULTIPLEXINGI/O See input/output.I/O bound See input/output bound.Iomega Corporation A major manufac-turer of removable storage media, bestknown for its popular Zip drive, which has2461book Page 198 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 204. 199IP over ATMshipped more than 12 million units world-wide.Iomegaalsomakesthehigher-capacityJaz drives, the Ditto line of tape-backupproducts, and Clik! storage devices for digi-tal cameras and hand-held computers.For more information on Iomega Corpora-tion, see See Integrated On-DemandNetwork.IOS See Internetworking OperatingSystem.IP See Internet Protocol.IP address The unique 32-bit numberthat identifies a computer on the Internet orsome other Internet Protocol network.An IP address is usually written (in decimal)as four numbers separated by dots or peri-ods and can be divided into two parts. Thenetwork address is made up from the high-order bits in the address, and the host ad-dress comprises the rest. In addition, thehost part of the address can be further sub-divided to allow for a subnet address.These numbers are very difficult for mostpeople to remember, so humans tend torefer to computers by their domain namesinstead.See also address classes; domain name;dotted decimal; Internet address; subnet.IPC See interprocess communication.ipconfig A utility program used to listvarious Internet Protocol configuration in-formation, including host address, subnetmask, and gateway addresses.See also IP address; netstat; Ping; subnetmask; tracert.IP datagram See Internet Protocol.IP Multicast An Internet standard thatallows a single host to distribute data tomultiple recipients.IP multicasting can deliver audio and videocontent in real time so that the person usingthe system can interact with the datastream. A multicast group is created, andevery member of the group receives everydatagram. Membership is dynamic; whenyou join a group, you start to receive thedatastream, and when you leave the group,you no longer receive the datastream.See also Internet Group Management Pro-tocol; multicast backbone; multicasting;streaming.IPng See IPv6.I-PNNI See Integrated-Private Network-to-Network Interface.IP over ATM A set of proposals that de-fine general methods of integrating InternetProtocol over an Asynchronous TransferMode (ATM) network, while preservingthe best features of the connectionless IPand connection-oriented ATM.These proposals have a variety of names, in-cluding layer 3 switching, high-speed rout-ing, short-cut routing, and multilayerswitching, and come from a variety ofsources, including the ATM Forum, the In-ternet Engineering Task Force, and a ven-dor collective known as Layer 3 Switching/Routing Advocates.See also IP switching.2461book Page 199 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 205. IPSec200IPSec A suite of protocols under develop-ment by the Internet Engineering TaskForce (IETF) designed to add security pro-visions to the Internet Protocol (IP). Alsoknown as IP Security.The Authentication Header (AH) ensuresthat the datagram has not been tamperedwith during transmission, and the Encapsu-lating Security Payload (ESP) defines en-cryption methods for IP data.IPSec operates in two modes:ITransport mode AH or ESP is placedimmediately after the original IP data-gram header and provides security be-tween two end systems such as a serverand a workstation.ITunnel mode The original IP datagramis placed inside a new datagram, and AHandESPareinsertedbetweentheIPheaderof the new packet and the original IP dat-agram. The new header points to the tun-nel endpoint, and the original headerpoints to the final destination of the data-gram. Tunnel mode is best suited to Virtu-al Private Network (VPN) use, securingremote access to your corporate networkthrough the Internet.See also encapsulation; Internet Protocol;ISAKMP/Oakley; tunneling; Virtual PrivateNetwork.IP security See IPSec.IP switching 1. A switch, developed byIpsilon Networks, that combines intelligentInternet Protocol (IP) routing with high-speed Asynchronous Transfer Mode (ATM)switching hardware. The IP protocol stack isimplemented on ATM hardware, allowingthe system to adapt dynamically to the flowrequirements of the network traffic as de-fined in the packet header.2. A technique that uses network-layer pro-tocols which provide routing services to addcapabilitiestolayer2switching.IPswitchinglocates paths in a network by using routingprotocols and then forwards packets alongthat route at layer 2. IP switching is designedfor networks that use switches rather thannetworks built around repeater hubs androuters.See also IP over ATM.IPv4 See Internet Protocol.IPv6 The next version of the Internet Pro-tocol, also called IP version 6 or IPng for IPnext generation.The most striking feature of IPv6 is that ituses a 128-bit address space rather than the32-bit system in use today. This providesfor a truly astronomical number of possibleaddresses. The address format consists of 8sections separated by colons. Each sectioncontains 16 bits expressed as 4 hexadecimalnumbers. An address might look like this:1234:5678:9ABC:DEF0:1234:5678:9ABC:DEF0In any address, one set of leading zeros canbe replaced by two colons.In addition to the 128-bit address space,IPv6 designates a 128-bit hierarchical ad-dress for point-to-point communicationcalled an Aggregatable Global Unicast Ad-dress Format (AGUAF). In this format, atop level aggregator (TLA) is assigned ablock of addresses by bodies such as the In-ternet Assigned Numbers Authority2461book Page 200 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 206. 201IPX internal network number(IANA). In turn, the TLA assigns addressesto a next level aggregator (NLA), which inturn assigns addresses to the site level ag-gregator (SLA). In turn, the SLA assignsblocks of contiguous addresses to its sub-scribers. The last level is the host interfaceID, which identifies a single host interface.Companies assign host interface IDs by us-ing a unique number on the subnet.IPv6 assigns addresses to interfaces, and be-cause a node can have multiple interfaces, itcan also have multiple IP addresses. A singleinterface can also have multiple addresses.An address can be multicast, unicast, oranycast, which is a special case of multicast.The IP datagram header has been simpli-fied, by dropping some fields and makingothers optional. IPv6 also allows for severaltypes of optional header extensions, someof which might be used for specialized han-dling instructions. In addition, IPv6 in-cludes the IPSec security extensions.See also Internet Protocol; IPSec.IP version 4 See Internet Protocol.IP version 6 See IPv6.IPv6IPX See Internetwork Packet eXchange.IPX address In Novell NetWare, a net-work address. Also known as an IPX inter-network address.The IPX address includes a 4-byte networknumberassignedtoeverysegmentonaLAN(the IPX external network number), a 6-byte node number that identifies a specificsystem and is usually derived from the inter-face card address originally assigned by themanufacturer, and a 2-byte socket number.See also IPX external network number.IPX external network number In Nov-ell NetWare, a hexadecimal number thatidentifies a network cable segment, as-signed when the NetWare InternetworkPacket eXchange (IPX) protocol is boundto a network interface board in the server.An IPX external network number can havefrom one to eight digits (1 to FFFFFFFE).IPX internal network number In No-vell NetWare, a hexadecimal number thatidentifies a NetWare server. Each server onthe network must have a unique Internet-work Packet Exchange (IPX) internalnetwork number. The number can havefrom one to eight digits (1 to FFFFFFFE)and is assigned to the server during Net-Ware installation.2461book Page 201 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 207. IPX internetwork address202IPX internetwork address See IPXaddress.IPXODI See Internetwork Packet Ex-change Open Data-Link Interface.IRC See Internet Relay Chat.IrDA See Infrared Data Association.IRF See Inherited Rights Filter.IRM See Inherited Rights Mask.IRQ See interrupt request.IRTF See Internet Research Task Force.ISA SeeIndustryStandardArchitecture;Integrated Services Architecture.ISAKMP/Oakley Abbreviation for Inter-net Security Association and Key Manage-ment Protocol/Oakley security key man-agement protocol. Also known as theInternet Key Exchange (IKE).A security protocol that automaticallymanages the exchange of secret symmetrickeys between sender and receiver.See also IPSec.ISDN See Integrated Services DigitalNetwork.ISO 10646 A 4-byte character encodingscheme that includes all the world’s nationalstandardcharacterencodings,definedbytheInternational Organization for Standardiza-tion (ISO). The 2-byte Unicode charactersset maps into a part of ISO 10646.See also American Standard Code for In-formation Interchange; double-byte char-acter set; Unicode.ISO See International Organization forStandardization.ISOC See Internet Society.isochronous service A method of trans-mitting real-time data using preallocatedbandwidth on a communications link, al-lowing time-synchronized transmissionswith very little delay. Isochronous service isrequired for real-time data such as synchro-nized voice and video, in which delays inpacket delivery would be unacceptable.Asynchronous Transfer Mode (ATM) canprovide isochronous service because its cellsare always the same size, so it is possible toguarantee accurate and timely delivery ofpackets. Other networks can provide isoch-ronous service by using a priority scheme todedicate bandwidth to video traffic.Iso-Ethernet The IEEE standard 802.9a,which describes a combination of Ethernetand Integrated Services Digital Network(ISDN) on the same cable.As well as providing standard 10MbpsEthernet connections over Category 3 orCategory 5 unshielded twisted-pair wiring,Iso-Ethernet also provides up to 96 ISDNBasic Rate B channels running at 64Kbpsconnected to internal or external users orsystems. One D channel is used for controland signaling information.The ISDN channels can be accessed over thenetwork via a single point of connection,which in turn is connected to the ISDN ser-vice; this removes the need for each work-station to have its own ISDN hardware.See also Integrated Services DigitalNetwork.2461book Page 202 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 208. 203IXCISO/OSI model See OSI ReferenceModel.ISP See Internet Service Provider.ISR Abbreviation for interrupt serviceroutine.See interrupt handler.ISV See Independent Software Vendor.ITU See International Telecommunica-tion Union.IXC See Interexchange Carrier.2461book Page 203 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 209. jabber204Jjabber A continuous and meaninglesstransmission generated by a network de-vice, usually the result of a user error or ahardware malfunction.Java A programming language and de-velopment environment created by SunMicrosystems, designed to create distrib-uted executable applications for use with aWeb browser containing a Java runtimeenvironment.Java technology has been licensed by liter-allyhundredsofcompanies,includingIBM,Microsoft, Oracle, Hewlett-Packard, andothers interested in developing Web-basedand platform-independent applications.The Java programming language is a porta-ble, object-oriented language, loosely mod-eled after C++, with some of the moretroubling C++ constructs such as pointersremoved. This similarity to C and C++ is noaccident; it means that the huge populationof professional programmers can quicklyapplytheirpreviousCexperiencetowritingcode in Java.Java is designed to support networking andnetworking operations right from the startand begins with the assumption that it cantrust no one, implementing several impor-tant security mechanisms.Java is architecturally neutral, does not careabout the underlying operating system, andis portable because it makes no assump-tions about the size of data types and ex-plicitly defines arithmetic behavior. Java isalso multithreaded to support differentthreads of execution and can adapt to achanging environment by loading classes asthey are needed, even across a network.Rather than writing code targeted at a spe-cific hardware and operating-system plat-form, Java developers compile their sourcecode into an intermediate form of bytecodethat can be processed by any computer sys-tem with a Java runtime environment. TheJava class loader transfers the bytecode tothe Java Virtual Machine (JVM), which in-terprets the bytecode for that specific plat-form. Java class libraries, those files thatmake up the standard application program-ming interface (API), are also loaded dy-namically. The runtime environment thenexecutes the application, which can runwithin a Web browser or as a stand-aloneapplication.See also bytecode; interpreter; Java ap-plet; Java Developer’s Kit; Java Virtual Ma-chine; just-in-time compiler; sandbox.2461book Page 204 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 210. 205Java Database ConnectivityJAVAJava applet A small program written inthe Java programming language designedto add a specific capability to a Web page.The applet is stored on the Web server andis downloaded to and executes within thebrowser.Java applets are inserted into a Web pageusing the <APPLET> tag, which indicates theinitial window size for the applet, variousparameters for the applet, and the locationfrom which the browser can download thebytecode file.Stand-alone programs written in the Javaprogramming language that can executewithout needing the browser are known asJava applications.See also bytecode; Java; Java Developer’sKit; Java Virtual Machine; just-in-timecompiler; sandbox.Java Database Connectivity Abbrevi-ated JDBC. An application programminginterface (API) that allows developers towrite Java applications that can access adatabase.2461book Page 205 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 211. Java Developer’s Kit206See also Open Database Connectivity.Java Developer’s Kit AbbreviatedJDK. A collection of software-develop-ment tools provided by Sun Microsystemsfor writing Java applications. This kit, dis-tributed free, contains a Java compiler, aninterpreter, a debugger, an applet viewer,and documentation.JavaScript A simple scripting languagecreated by Netscape Communications andSunMicrosystemsthatallowsdeveloperstoadd a specific capability to a Web page.JavaScript is relatively easy to write whencompared with the Java programminglanguage, but it is slower in execution andhas far fewer application programminginterface (API) functions available. AJavaScript-compliant Web browser, suchas Netscape Navigator, is necessary to runthe JavaScript code.See also Java; script.JavaSoft A subsidiary of Sun Micro-systems responsible for developing andpromoting the Java programming lan-guage and related products.For more information on JavaSoft, Virtual Machine The runtime en-vironment for Java applets and applica-tions; sometimes abbreviated JVM.The Java Virtual Machine creates a simu-lated environment that provides the sameinterface to applications, no matter whathardware and operating system combina-tion is in use.The Java Virtual Machine consists of twolayers:IThe top layer is compatible with all Javaapplications.IThe bottom layer is compatible with aspecific computing platform, such as theIntel family of processors.See also Java.JDBC See Java Database Connectivity.JDK See Java Developer’s Kit.Jini A technology from Sun Microsys-tems that is based on Java concepts and thatallows spontaneous networking of a largevariety of network devices.Jini creates a federation of Java Virtual Ma-chines on a network and allows users, de-vices, data, and applications to connectdynamically to share information and toperform tasks without prior knowledge ofone another’s capabilities.See also Java.JIT compiler See just-in-time compiler.jitter A type of distortion found on ana-log communications lines that results indata-transmission errors.job A unit of work done by a computer,usually in a mainframe environment. A jobcan be the one-time execution of a single fileor the execution of a whole series of pro-grams to accomplish a complex task.See also job control.job control A mechanism used to man-age jobs, allowing them to be started,2461book Page 206 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 212. 207JVMstopped, and moved between the back-ground and the foreground.Joint Photographic Experts GroupAbbreviated JPEG; also sometimes abbre-viated JPG. An image-compression stan-dard and file format that defines a set ofcompression methods for high-quality im-ages such as photographs, single videoframes, or scanned pictures. JPEG does notwork very well when compressing text, lineart, or vector graphics.JPEG uses lossy compression methods thatresult in some loss of the original data.When you decompress the original image,you don’t get exactly the same image thatyou started with, although JPEG was spe-cifically designed to discard informationnot easily detected by the human eye.JPEG can store 24-bit color images in asmany as 16 million colors; files in GraphicsInterchange Format (GIF) form can onlystore 256 colors.See also Graphics Interchange Format;lossy compression.JPEG See Joint Photographic ExpertsGroup.JPG See Joint Photographic ExpertsGroup.jukebox A high-capacity storage devicethat uses an autochanger mechanism tomount or dismount disks automatically. Ajukebox typically contains as many as 50disks and a mechanism that picks up disksfrom a bay and loads them into the drives asthey are needed.See also high-capacity storage system.Julian date A method of representingthe date that is often used in computer sys-tems. The first digit represents the year, andthe remaining digits represent the day of theyear, counting from January 1.See also Y2K problem.jumper A small plastic and metal connec-tor that completes a circuit, usually to selectone option from a set of several user-defin-able options. Jumpers are often used to se-lect one particular hardware configurationfrom a choice of configurations.junction point In Microsoft Windows2000, a drive or disk partition attached toan empty folder on an NTFS volume. Usingjunction points allows you to mount morethan 26 (A–Z) storage volumes.See also mounted drive.just-in-time compiler Sometimes ab-breviated JIT compiler. A compiler that re-ceives the bytecode of a Java applicationand compiles the bytecode on the fly.Java bytecode processed by a just-in-timecompiler executes faster than the samebytecode processed by a Java VirtualMachine.See also Java; Java Virtual Machine.JVM See Java Virtual Machine.2461book Page 207 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 213. K208KK See kilo-.K56Flex A modem technology fromRockwell Semiconductor Systems and Lu-cent Technologies that provides up to56Kbps downstream and up to 40Kbps up-stream. Replaced by the V.90 standard.See also V.90; X2.Kb See kilobit.KB See kilobyte.Kbit See kilobit.Kbps See kilobits per second.Kbyte See kilobyte.KCC See Knowledge ConsistencyChecker.keep-alive signal A signal transmittedto maintain a communications circuit dur-ing periods of idleness and to prevent thecircuit from timing out and terminating theconnection.Kerberos A network security system de-veloped as a part of Project Athena at MIT.Kerberos is used to authenticate a user whois asking for permission to use a particularnetwork service.Kerberos can be used to control the initialconnection to a server or to authenticate ev-ery single request between a client and theserver. It grants tickets to a client to allowthe use of a specific service and is secureeven on a nonsecure network.Kerberos takes the following precautions:IPasswords are never sent over the networkunencrypted, making it impossible for net-work snoopers to capture passwords.IAllKerberosmessagesaretimestampedsothat they cannot be captured and then re-played at a later time; Kerberos does notaccept old messages.IWhen you request access to a service, toaccess a file server, for example, Kerberosgives you a “ticket” that is valid for accessto the file server but not valid for any oth-er service. When you try to connect to theserver, you send your ticket with the re-quest. Once the server knows who youare, the server decides whether to grantyou access. Tickets also expire, and if yoursession lasts longer than the predefinedlimit, you will have to reauthenticateyourself to Kerberos to get a new ticket.Kerberos is named after the three-headeddog Cerberus, who guards the gates of theunderworld in Greek mythology.See also authentication; certificate; digitalsignature.Kerberos Distribution Center Abbre-viated KDC. In Microsoft Windows 2000Server, a Kerberos function that runs on ev-ery domain controller and controls the dis-tribution of Kerberos keys and tickets.See also Kerberos.KDC See Kerberos Distribution Center.2461book Page 208 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 214. 209kilo-Kermit A file-transfer protocol devel-oped at Columbia University and placed inthe public domain that is used to transferfiles between PCs and mainframe comput-ers over standard telephone lines.Data is transmitted in variable-length blocksup to 96 characters in length, and each blockis checked for transmission errors. Kermitdetects transmission errors and initiates re-peat transmissions automatically.See also Xmodem; Ymodem; Zmodem.kernel The fundamental part of an oper-ating system. The kernel stays resident inmemory at all times, often hidden from theuser, and manages system memory, the filesystem, and disk operations.The kernel also runs processes and providesinterprocess communications betweenthose processes, including synchronizingevents, scheduling, passing messages, man-aging input and output routines, and man-aging memory.See also Linux; Mach, microkernel, shell.key 1. An entry in the Microsoft Win-dows Registry that contains an element ofconfiguration information. A key may alsobe empty and have no value set.2. In encryption, a mechanism used to en-code a message.3. In a database system, a unique valueused to identify data records. Also knownas a primary key.See also public key encryption; sub-key.keyboard buffer A small amount of sys-tem memory used to store the most recentlytyped keys, also known as the type-aheadbuffer. Some utilities or shells let you collecta number of keystrokes or commands andedit or reissue them.keyboard template A plastic card thatfits over certain keys (usually the functionkeys) on the keyboard as a reminder of howto use them. These templates are specific toan application, and they can be a useful re-minder for new or occasional users.key combination In menu-driven andgraphical user interfaces, some menu com-mands can be executed by certain combina-tions of keystrokes, also known as shortcutkeystrokes. By using key combinations, us-ers can bypass the menus and so speed upoperations.keypass attack See brute-force attack.keyspace attack See brute-forceattack.key redefinition The ability of an appli-cation to assign different functions to spe-cific keys.keystroke The action of pressing andthen releasing a key on the keyboard to ini-tiate some action or enter a character.keyword Any of the words, sometimesknown as reserved words, that make up thevocabulary of a particular programminglanguage or set of operating system com-mands and utilities.kilo- A prefix indicating 1000 in the met-ric system. Because computing is based onpowers of 2, kilo usually means 210, or1024. To differentiate between these twouses, a lowercase k is used to indicate 10002461book Page 209 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 215. kilobaud210(as in kHz), and an uppercase K is used toindicate 1024 (as in KB).See also mega-.kilobaud One thousand baud. A unit ofmeasurement of the transmission capacityof a communications channel.See also baud.kilobit Abbreviated Kb or Kbit. 1024 bits(binary digits).See also gigabit; megabit.kilobits per second Abbreviated Kbps.The number of bits, or binary digits, trans-mitted every second, measured in multiplesof 1024 bits per second. Used as an indica-tor of communications transmission rates.See also megabits per second.kilobyte Abbreviated K, KB, or Kbyte.1024 bytes.See also exabyte; gigabyte; megabyte;petabyte; terabyte.kluge Pronounced “klooj.” A programthat doesn’t work as well as it should, is notcarefully designed, and is not well written.A kluge may also be a program that works,but for all the wrong reasons, or only undervery specific, highly unrealistic conditions.See also hack.Knowledge Consistency CheckerAbbreviated KCC. In Microsoft Windows2000 Server, an Active Directory functionthat monitors and configures replicationconnection objects between domain con-trollers.Korn shell An upward-compatible ex-tension to the original Unix shell, writtenby David Korn and released as part of Sys-tem V.The Korn shell is now the default shell onmany Unix systems, particularly thosebased on System V, including UnixWareand many others.Because the Korn shell is an extension of theBourne shell, everything that works intheBourneshellalsoworksintheKornshell.The Korn shell also adds the following:IInteractive editing of the command linewith either vi or emacsIBetter function definitions providing localvariables and the ability to create recur-sive functionsIExtensive pattern matching for filenames,similar to regular expressionsSeveral features were adapted from the Cshell, including:ICommand history allowing retrieval andreuse of previous commandsIJob control and the mechanism for mov-ing jobs between the background and theforegroundIAliases for abbreviated command namesIThe tilde (~) used as a shorthand for thename of the home directorySee also Bash shell; Bourne shell; C shell;Unix shell.2461book Page 210 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 216. 211LAN EmulationLL2 Cache See secondary cache.L2TP See Layer 2 Tunneling Protocol.LAN See local-area network.LANalyzer for Windows A MicrosoftWindows-based software product fromNovell used to troubleshoot and monitornetwork performance and activity.The LANalyzer main screen is a dashboardof gauges displaying real-time statistics, in-cluding LAN utilization, packets per sec-ond, and errors per second. User-specifiedalarms can also be set on these gauges, anddetailed statistics screens plot frame rate,utilization, and error rate over time.LAN-aware An application that con-tains mechanisms for file and record lock-ing to prevent multiple simultaneousaccess when used on a network. The termis often applied in a broader sense to anyapplication capable of running in a net-worked environment.LANDesk Management Suite A pack-age of network management utilities fromIntel Corporation that includes hardwareand software inventory, server monitoring,client monitoring and control, networktraffic monitoring, virus protection, remoteaccess, remote control, and print-queuemanagement.LANDesk also includes a Desktop Manage-ment Interface (DMI) remote managementconsole and DMI desktop agents or servicelayers for MS-DOS and Windows clients.See also Desktop Management Interface.LAN Distance A hardware/softwarecombination product from Network Com-munications Corp. used to troubleshootand monitor performance and activity onEthernet and token-ring LANs.The LAN Distance hardware includes an on-boardprocessorandalargebufferforpacketcapturing. The package can decode mostLAN protocols in common use, includingNetWare, TCP/IP, DECnet, Banyan, Net-work File System (NFS), AppleTalk FilingProtocol (AFP), Open Systems Interconnect(OSI), Systems Network Architecture(SNA), NetBEUI, Xerox Network Services(XNS), and Server Message Block (SMB).LANE See LAN Emulation.LAN Emulation Abbreviated LANE. AnAsynchronous Transfer Mode (ATM) spec-ification that defines ways of connectinglegacy local-area networks such as Ethernetand token ring to an ATM backbone, al-lowing ATM to replace older and slowerbackbone circuits.LANE provides the translation servicesneeded between the two types of networksand is totally transparent to the high-levelprotocols. LANE consists of four majorcomponents:IBroadcast and unknown server (BUS),which manages address resolution.2461book Page 211 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 217. LANRover212ILAN Emulation Client (LEC), which runson all nodes connected to the ATM net-work, initiates data transfers betweenother clients, and makes mapping re-quests between MAC (media access con-trol) addresses and ATM addresses.ILAN Emulation Configuration Server(LECS), which provides configurationinformation and tracks on which virtualLAN each LAN Emulation Clientoperates.ILAN Emulation Server (LES), which pro-vides address mapping between MAC ad-dresses and ATM addresses and usuallyruns on the same node as the BUS.See also Asynchronous Transfer Mode; In-tegrated-Private Network-to-Network In-terface; IP over ATM; IP switching.LANRover A remote access packagefrom Shiva Corporation that lets networkusers log in from their PC or portable com-puter when away from the office.LAN Server An IBM network operatingsystem, based on a version of OS/2, thatruns on Intel processors as well as on thePowerPC.LAN Server supports Microsoft Windows,MS-DOS, OS/2, and Macintosh clients aswell as AppleTalk, IPX/SPX, TCP/IP, andNetBIOS protocols. LAN Server supportsdomain directory services and encryptedpasswords, but does not include C-2 levelcertification.LANtastic A popular peer-to-peer net-work operating system, from Artisoft, Inc.,that runs with MS-DOS, OS/2, or MicrosoftWindows and supports Microsoft Win-dows,MS-DOS,OS/2,Macintosh,andUnixclients.The network can be run with all stationssharing files with all other stations or, forenhanced performance, with one PC actingas a dedicated file server. LANtastic sup-ports an unlimited number of users, in-cludes built-in CD-ROM, network e-mail,and network fax support, scheduling andnetwork management, file-level security,and Internet access and can connect easilyinto the NetWare environment.LAN WorkGroup Novell’s connectivitypackage that is located and managed cen-trally from the NetWare file server.The system includes transparent file sharing,terminal emulation, remote command exe-cution, and printer-redirection features forboth MS-DOS and Windows clients. TheLAN WorkGroup differs from its stand-alone counterpart, LAN WorkPlace, in thatit can be managed from the file server.See also LAN WorkPlace.LAN WorkPlace Novell’s connectivitysoftware for MS-DOS and Windows cli-ents. Features include terminal emulation,transparent Network File System (NFS) filesharing, and a Web browser.See also LAN WorkGroup.LAP See Link Access Procedure.LAP-B See Link Access Procedure-Balanced.LapLink A popular communicationspackage from Traveling Software, used to2461book Page 212 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 218. 213Layer 2 Tunneling Protocoltransfer and synchronize files between alaptop computer and a desktop or net-worked computer.LAPM See Link Access Procedure forModems.laptop computer A small, portablecomputer that is light enough to carry com-fortably, with a flat screen and keyboardthat fold together.Advances in battery technology allow lap-top computers to run for many hours be-tween charges. Laptop computers oftenhave a thin, backlit or sidelit liquid-crystaldisplay (LCD) or a plasma screen. Somemodels can mate with a docking station toperform as a full-sized desktop system backat the office, and many new laptop comput-ers allow direct connection to the networkwith PCMCIA network interface cards. Insome laptop computers, a set of businessapplications is built in to ROM.See also hand-held computer; mobilecomputing; notebook computer; PC Mem-ory Card International Association; portreplicator; wireless communications.Large Internet Packet AbbreviatedLIP. A mechanism that allows the NovellNetWare internetwork packet size to be in-creased from the default 576 bytes, thus in-creasing throughput over bridges androuters.LIP allows workstations to determine thepacket size based on the largest packet sup-ported by the router; the larger packet sizeis also supported by Ethernet and token-ring networks.last known good configuration In Mi-crosoft Windows NT, the last configurationthat was used to boot the computer success-fully. Windows NT saves this configurationand offers it as a startup option during theboot process.last mile A term, not to be taken too lit-erally, that describes the link between a cus-tomer site and the telephone company’scentral office. This link is often the most ex-pensive and least efficient connection in thetelephone company’s system and is often abarrier to high-speed services.latency The time delay involved in mov-ing data traffic through a network. Latencycan arise from several sources:IPropagation delay, which is the time ittakes the data to travel the length of theline.ITransmission delay, which is the time ittakes to move the data across the networkmedia.IProcessing delay, which is the time it takestoestablishtheroute,encapsulatethedata,and take care of other switching tasks.See also propagation delay.Layer 2 Tunneling Protocol Abbrevi-ated L2TP. A proposed standard for asecure, high-priority, temporary communi-cations path through the Internet.L2TP is based on Cisco’s Layer 2 Forward-ing (L2F) protocol and includes featuresfrom Microsoft’s Point-to-Point TunnelingProtocol (PPTP). A tunnel is establishedfrom an Internet Service Provider (ISP) to acorporate site, and information is transmit-ted through the tunnel. Once L2TP is set up,2461book Page 213 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 219. LCD214the user communicates with the corporatesystem through what seems to be a directdial-up connection; the ISP is effectively re-moved from the picture.See also tunneling.LCD See liquid-crystal display.LCD monitor A monitor that uses liq-uid-crystal display (LCD) technology.Many laptop and notebook computers useLCD monitors because of their low powerrequirements.LDAP See Lightweight DirectoryAccess Protocol.leaf object InNovellNetWareDirectoryServices (NDS), an object that cannot con-tain any other objects; also known as a non-container object. Leaf objects can be print-ers, servers, print queues, or even users.See also container object.Learning Tree International A majorprovider of training classes and computer-technology certifications. Learning Tree In-ternational offers more than 150 network-ing and computer-related training classes inthe United States, Europe, and Asia, as wellas 27 professional certification programs.For more information about Learning TreeInternational, see Tree International CertifiedProfessional Aprofessionalcertificationfrom Learning Tree International, availablewith a large number of subject specializa-tions, including Local Area Networks,Wide Area Networks, Internetworking, PCService and Support, and Unix Systems.See also Learning Tree International.leased line A communications circuit ortelephone line reserved for the permanentuse of a specific customer; also called a pri-vate line.See also dedicated line.LEC See Local Exchange Carrier.legacy application An application de-signed to run on what has now become alegacy system and that continues to be used.A legacy application may perform admira-bly and provide little reason to upgrade toa more up-to-date system, or it may be in-efficient, perform poorly, and continue inuse because replacing it is simply tooexpensive.See also legacy system; legacy wiring.legacy system A computer system, de-veloped to solve a particular business need,which, due to the passage of time, has be-come obsolete.Legacy systems do not conform to the tech-nical standards or performance standardsof up-to-date systems. There is usually a re-quirement to maintain backward compati-bility with or connections to legacy systems.legacy wiring Preinstalled wiring thatmay or may not be suitable for use with anetwork.See also legacy system.2461book Page 214 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 220. 215line adapterLempel-Ziv-Welch Abbreviated LZW,an algorithm used in data compression,developed by Abraham Lempel, Jacob Ziv,and Terry Welch.LZW is a general-purpose compression al-gorithm suitable for use on almost any typeof data. It is fast in both compressing anddecompressing data and does not requirethe use of floating-point operations.LZW is a lossless compression method andis used in several image formats such asGraphics Interchange Format (GIF) andTag Image File Format (TIFF), as well as apart of the V.32 bis modem compressionstandard and PostScript Level 2.The patent for LZW compression is held byUnisys, which levies a fee on any applicationthat uses the LZW compression algorithm.See also lossless compression; lossycompression.level 2 cache A secondary static RAMcache located between the primary cacheand the rest of the system. A level 2 cache isoften larger than the primary cache, and itis usually slower. In Intel’s Pentium II pro-cessor, the level 2 cache is implemented as apart of the package that holds the CPU.See also cache; memory cache.Lexmark International, Inc. A majormanufacturer of printers, based in Lexing-ton, Kentucky; spun off from IBM in 1991.Lexmark markets laser and ink jet printersfor both home and office use, as well as laser-printer management software for servers.For more information on Lexmark Interna-tional, Inc., see www.lexmark.comLF See line feed.light-wave communications Usuallyrefers to communications using fiber-opticcables and light generated by light-emittingdiodes (LEDs) or lasers.Lightweight Directory Access Pro-tocol Abbreviated LDAP. A directoryservices specification that has recentlygained wide acceptance.A directory service provides “white page”service for an organization to help peoplefind other people and network services andcan also be used over the Internet. A direc-tory service is a database that can be ma-nipulated in a variety of ways to providethis information.LDAP can be used as a directory service byitself, or it can be used for “lightweight” ac-cess to an X.500-compliant directory ser-vice. LDAP is a subset of X.500 that runsover TCP/IP; X.500 runs on OSI-compliantsystems. Many companies have announcedtheir intention to support LDAP in upcom-ing products.See also Active Directory; Novell DirectoryServices; X.500.LIM EMS See Expanded modem See linedriver.line adapter In communications, adevice that converts a signal into a formsuitable for transmission over a communi-cations channel.A modem is a specific type of line adapterused to convert the computer’s digital2461book Page 215 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 221. line analyzer216signals into analog form so that they can betransmitted over a telephone line.line analyzer Any device that monitorsand displays information about a transmis-sion on a communications channel. A lineanalyzer is used for troubleshooting andload monitoring.line-of-business application Seemission-critical application.line driver In communications, a hard-ware device used to extend the transmissiondistance between computers that are con-nected using a serial interface based on theRS-232 standard. A line driver is requiredat each end of the line. Also known as abaseband modem, limited-distance mo-dem, or short-haul modem.See also short-haul modem.line feed Abbreviated LF. A printer com-mand that advances the paper in the printerby one line, leaving the print head in thesame position. In the ASCII character set, aline feed has a decimal value of 10.See also American Standard Code forInformation Interchange; carriage return;Extended Binary Coded Decimal Inter-change Code.line printer Anyhigh-volumeprinterthatprints a complete line at a time, rather thanprinting one character at a time (as a dot-ma-trix printer or a daisy-wheel printer does) orone page at a time (as a laser printer does).Line printers are very high-speed print-ers and are common in mainframeenvironments.line-sharing device A small electronicmechanism that allows a fax machine and atelephone answering machine to share thesame phone line. The device answers thecall and listens for the characteristic high-pitched fax carrier signal. If this signal isdetected, the call is routed to the fax ma-chine; if it is not present, the call is sent toa telephone or answering machine.line-of-sight An unobstructed path be-tween the transmitter and receiver. Laser,microwave, and infrared transmissionsusually require a clear line-of-sight.See also wireless communications.line speed In communications, thetransmission speed that a line will reliablysupport for any given grade of service.See also connection speed; On a Web page or a hypertext docu-ment, a connection between one elementand another in the same or in a differentdocument.Link Access Procedure AbbreviatedLAP. The link-level protocol specified bythe CCITT X.1 recommendation used forcommunications between DCE (data com-munications equipment) and DTE (dataterminal equipment).See also Consultative Committee for Inter-national Telephony and Telegraphy; LinkAccess Procedure-Balanced.Link Access Procedure-Balanced Ab-breviated LAP-B. A common CCITT bit-oriented, data-link layer protocol used to2461book Page 216 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 222. 217Linuxlink terminals and computers to packet-switched networks. It is equivalent to theHDLC (High-level Data Link Control)asynchronous balanced mode, in which astation can start a transmission without re-ceiving permission from a control station.Link Access Procedure for ModemsAbbreviatedLAPM.Thedata-linkprotocolused by V.32 error-correcting modems.When two LAPM modems connect, theytransmit data in frames using bit-orientedsynchronous techniques, even though theattached computer communicates with themodem as a standard asynchronous device.See also Link Access level Part of the CCITT’s X.25 stan-dard that defines the link protocol. LAP(Link Access Procedure) and LAP-B (LinkAccess Procedure-Balanced) are the link ac-cess protocols recommended by CCITT.See also Consultative Committee for Inter-national Telephony and rot A slang expression used to de-scribe an out-of-date URL on a Web page.Link rot occurs when the page indicated bythe link is moved or erased.See also link; Uniform Resource routing algorithm A rout-ing algorithm in which each router broad-casts information about the state of thelinks to all other nodes on the internetwork.This algorithm reduces routing loops buthas greater memory requirements than thedistance vector algorithm.See also distance vector algorithm; OpenShortest Path layer Abbreviated LSL.An implementation of the Open DatalinkInterface (ODI) that works between theNetWare server’s LAN drivers and com-munications protocols, such as IPX (Inter-net Packet eXchange) or TCP/IP, allowingnetwork interface cards to service one ormore protocol stacks. LSL is also used onworkstations.See also multiple-link interface driver;Open Data-link Interface/Network DriverInterface Specification Support.Linux A free, Unix-compatible, 32-bitoperating system developed in 1991 by Li-nus Torvalds while at the University of Hel-sinki in Finland.Strictly speaking, Linux is the name of theoperating system kernel, the central part ofthe operating system that manages systemservices, but many people use the name torefer to the complete operating systempackage, including utilities, editors andcompilers, games, and networking compo-nents. Many of these important elementsare actually part of the Free Software Foun-dation’sGNUProject,andothershavebeenwritten and released by volunteers.Linux is supported and distributed by com-panies such as Red Hat Software, CalderaSoftware, Workgroup Solutions, WalnutCreek Software, and S.u.S.E. of Germany.With the increasing use of Linux in the cor-porate world, several major companieshave announced some level of support forthe operating system, including Hewlett-Packard, Silicon Graphics, Sun Microsys-tems, and Intel, and several major applica-tions packages have been ported to Linux,2461book Page 217 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 223. LIP218including Oracle’s Oracle8, Adaptive Serv-er Enterprise from Sybase, and IBM’s DB2.See also Free Software Foundation; opensource software.LIP See Large Internet Packet.liquid-crystal display AbbreviatedLCD. A display technology common in por-table computers that uses electric current toalign crystals in a special liquid.The rod-shaped crystals are containedbetween two parallel, transparent elec-trodes. When current is applied, the elec-trodes change their orientation, creating adark area. Many LCD screens are alsobacklit or sidelit to increase visibility andreduce eyestrain.LISTSERV A mailing list product avail-able from L-Soft International, Inc. LIST-SERV runs on Unix, Microsoft Windows,and several other operating systems.See also listserver; mailing list.listserver An automatic mailing systemavailable on the Internet.Rather than sending e-mail on a particulartopic to a long list of people, you send it toa special e-mail address, where a programautomatically distributes the e-mail to allthe people who subscribe to the mailing list.Several programs have been written to au-tomate a mailing list; the most common iscalled LISTSERV, but you may also en-counter mailserv, majordomo, or almanac.Mailing lists are usually devoted to a specificsubject, such as training dogs or playingobscure types of bagpipes, rather than togeneral interest communications.See also LISTSERV; mailing list; news-group; Usenet.little endian A computer architecture inwhich the least significant byte has the low-est address and so is stored little end first.Many processors, including those from In-tel, the PDP-11, and the VAX family ofcomputers, are all little endian. The termcomes from Swift’s Gulliver’s Travels, inwhich wars were fought over whetherboiled eggs should be opened at the big endor the little end.See also big endian; holy wars.liveware Aslangtermforthepeoplewhouse computers, as distinct from hardware,firmware, or software.LLC See logical link control.loadable module In Novell NetWare, aprogram that can be loaded and unloadedfrom the server or workstation while theoperating system is running.Two common types of loadable modulesare NetWare Loadable Modules (NLMs),which are run on the server, and VirtualLoadable Modules (VLMs), which run on aworkstation.See also NetWare Loadable Module; Virtu-al Loadable Module.load average Onemeasureofhowmuchwork the CPU is doing; defined as theaverage number of jobs in the run queueplus the number of jobs that are blocked2461book Page 218 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 224. 219Local Procedure Callwhile waiting for a disk access. This mea-surement is usually taken at 1-, 5-, and 15-minute intervals during a 24-hour period togive useful information.See also uptime.load balancing A technique that dis-tributes network traffic along parallelpaths to make the most efficient use of theavailable bandwidth while also providingredundancy. Load balancing will automat-ically move a user’s job from a heavilyloaded network resource to a less-loadedresource.See also clustering.load sharing The ability of two or moreremote bridges to share their load in a par-allel configuration. If a bridge fails, traffic isrouted to the next parallel bridge.local-area network Abbreviated LAN.A group of computers and associated pe-ripheral devices connected by a communi-cationschannel,capableofsharingfilesandother resources among several users.See also file server; metropolitan-area net-work; peer-to-peer network; wide-area net-work; zero-slot LAN.local bus A PC bus specification that al-lows peripheral devices to exchange data ata rate faster than the 8MBps allowed by theISA (Industry Standard Architecture) defi-nition and the 32MBps allowed by the EISA(Extended Industry Standard Architecture)definition.Local bus capability must be built into thesystem’s motherboard right from the start;it is not possible to convert an ISA-, EISA-,or MCA (Microchannel Architecture)-based computer into a local-bus system.local disk In networking, a disk drive onyour workstation or PC, rather than a driveavailable to you over the network.See also network drive.local drive See local disk.Local Exchange Carrier AbbreviatedLEC. A term coined from the Telecommu-nications Act of 1996 to describe the localtelephone company that provides localtransmission and switching services.See also Competitive Local Exchange Car-rier; Incumbent Local Exchange Carrier.local group In Microsoft Windows NTServer, a group granted rights and permis-sions to only the resources on the servers ofits own domain.See also global group.local loop That part of a communica-tions circuit that connects subscriber equip-ment to equipment in a local telephoneexchange. This link is often the most expen-sive and least efficient connection in thetelephone company’s system and is often abarrier to high-speed services.See also last mile.local printer In networking, a printer at-tached to a workstation or a PC, rather thanto the file server or a print server.Local Procedure Call AbbreviatedLPC.An interprocess communications methodused in multitasking operating systems thatallows tasks running concurrently to talk to2461book Page 219 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 225. local security authority220each other. LPCs allow tasks to share mem-ory space, synchronize tasks, and pass mes-sages to one another.See also interprocess communication;pipe; Remote Procedure Call; socket.local security authority In MicrosoftWindows NT, a security subsystem thatmanages the security policy on the localcomputer and provides user authenticationservices to other operating system compo-nents that need access to that information.LocalTalk Theshieldedtwisted-pair(STP)wiring and connectors available from Applefor connecting Macintosh computers usingthe built-in AppleTalk network hardware.See also AppleTalk.local user profile A user profile that isspecific to the computer upon which it wascreated; a local user profile does not followthe user if he or she logs on to a differentcomputer.See also mandatory user profile; roaminguser profile.locational organization A way of orga-nizing the Novell Directory Services (NDS)Directory tree that divides it into Organiza-tional Units for each geographical locationin a company.See also Organizational Unit.locked file A file that you can open andread, but not write to, delete, move, re-name, or change in any way.logical drive The internal division ofa large hard disk into smaller units. Onesingle physical drive may be organized intoseveral logical drives for convenience, witheach one appearing to the user as a sepa-rate drive.logical link control Abbreviated LLC.The upper component of the data-link layerthat provides data repackaging functionsfor operations between different networktypes.The media access control is the lower com-ponent that gives access to the transmissionmedium itself.See also data-link layer; media accesscontrol.logical unit Abbreviated LU. A suite ofprotocols developed by IBM to controlcommunications in an SNA (Systems Net-work Architecture) network, as follows:ILU type 0 Uses SNA transmission con-trol and flow-control layers.ILU type 1, LU type 2, and LU type 3Control host sessions for IBM 3270 ter-minals and printers.ILU type 4 Supports peer-to-peer andhost-to-device communications betweenperipheral nodes.ILU type 6.1 Supports a communica-tions session for IBM databases and trans-action management systems.ILU type 6.2 The peer-to-peer protocolof Advanced Program-to-Program Com-munications. It also features comprehen-sive end-to-end error processing and ageneralizedapplicationprograminterface(API).2461book Page 220 Thursday, May 4, 2000 11:59 AMCopyright © 2000 SYBEX Inc., Alameda, CA.
  • 226. 221long filenameILU type 7 Data Stream terminals usedon AS/400 systems.See also Advanced Program-to-ProgramCommunications; physical unit.logical unit number Abbreviated LUN.The logical address of a Small ComputerSystem Interface (SCSI) device when severaldevices are attached to a single SCSI deviceID. The LUN is usually set to zero unless theSCSI adapter supports multiple LUNs on asingle SCSI device ID.See also Small Computer SystemInterface.logic bomb A sabotage attack on a sys-tem timed to go off at some time in the fu-ture; essentially a Trojan Horse with a fuse.A logic bomb goes off at a certain time orwhen triggered by a certain event and thenperforms some operation. It might release avirus, delete files, or send comments to aterminal. An unhappy programmer mayplant a logic bomb on a system and time itto go off long after she has left the companyso as to avoid suspicion.See also boot sector virus; file-infectingvirus; macro virus; multipart virus; poly-morphic virus; stealth virus; Trojan Horse;vaccine.log in See log on.LOGIN directory In Novell NetWare,the SYS:LOGIN directory, created duringthe network installation, that contains theLOGIN and NLISTutilities used to supportusers who are not yet authenticated.login script A small file or macro thatexecutes the same set of instructions everytime a user logs on to a computer system ornetwork. Sometimes called a logon script.Login scripts can map drives, display mes-sages, set environment variables, and runprograms and are critical for proper config-uration of each user’s network environment.A communications script may send theuser-identification information to an onlineinformation service each time a subscriberdials up the service.See also script.log off To terminate a session and signoff a computer system by sending an endingmessage. Also known as logoff and log out.The computer may respond with its ownmessage, indicatin