The Information-Processing MachineLike the Analytical Engine, the computer is a machine that changesinformation from one form to another. All computers take ininformation (input) and give out information (output).The computer’s flexibility isn’t hidden in hardware—the physicalparts of the computer system. The secret is software, or programs—the instructions that tell the hardware what to do to transformthe input data (information in a form that it can read) into thenecessary output.Evolution and AccelerationComputer hardware evolved rapidly, with new technologies replacingold every few years. People sometimes refer to four generations ofcomputers based on the vacuum tube, the transistor, the integratedcircuit, and the microprocessor. Each of these new technologiesresulted in computer systems that were more reliable, smaller,faster, more efficient, and cheaper.Moore’s Law in 1965 predicted that the power of a silicon chip ofthe same size would double about every 18 months; this predictionhas been remarkably accurate ever since.
The Microcomputer RevolutionA microprocessor contains the critical components of a computer on asilicon chip. Thanks to the microprocessor, the microcomputerrevolution began in the mid-1970s with the introduction of low-cost,typewriter-sized computers as powerful as many of the room-sizedcomputers that had come before.Personal computers, or PCs, as microcomputers have come to beknown, are now everyday tools in offices, factories, homes, andschools.Mainframes and SupercomputersBefore the microcomputer revolution, most information processingwas done on mainframe computers—room-sized machines withprice tags that matched their size. Today, large organizations still usemainframes for big computing jobs.Travel agents and bank tellers communicate with a mainframe usinga computer terminal—a combination keyboard and screen thattransfers information to and from the computer. Mainframecomputers are capable of communicating with several userssimultaneously through a technique called timesharing.
Workstations and PCsServers are computers especially designed to provide software andother resources to other computers over a network.A workstation is a high-end desktop computer with thecomputing power of a minicomputer at a fraction of the cost.Workstations are widely used by scientists, engineers, Wall Streetanalysts, animators, and others whose work involves intensivecomputation. Personal computers are less powerful and lessexpensive than workstations, but the line between the twocategories is growing blurry.
Portable ComputersToday, one of the fastest growing segments of the PC marketinvolves machines that aren’t tied to the desktop—portablecomputers. Portability is a relative term.Flat-screen, battery-powered laptop computers are light enough torest on your lap while you work or carry like a small briefcase whenclosed.Embedded Computers and Special-Purpose ComputersNot all computers are general-purpose machines. Many are special-purpose (dedicated) computers that perform specific tasks,ranging from controlling the temperature and humidity in a high-rise office building to monitoring your heart rate while you work out.Embedded computers enhance all kinds of consumer goods:wristwatches, game machines, stereos, videocassette recorders(VCRs), ovens, and even automobiles. Embedded computers are alsowidely used in industry, the military, and science for controlling avariety of hardware devices, including robots.When a program is immortalized on a silicon chip it becomesfirmware—a hybrid of hardware and software.
COMPUTER CONNECTIONSTHE INTERNET REVOLUTIONWhile the world was still reeling from the impact of themicrocomputer revolution, another information technologyrevolution was quietly building up steam: a network revolution.If current trends continue, we’ll look back on the 1990s as theend of the personal computing era and the beginning of theinterpersonal computing era.The Emergence of NetworksThe first computers were large, expensive, self-containedmachines that could process only one job at a time. Theinvention of timesharing in the 1960s allowed multiple users toconnect to a single mainframe computer through individualterminals. When personal computers started replacingterminals, they were often linked together in local areanetworks so they could share scarce, expensive resources.
The Internet ExplosionA few visionary computer scientists and engineers, with financialbacking from the U.S. government, built an experimental networkcalled ARPANET in 1969. This groundbreaking network wouldbecome the Internet—the global collection of networks that isradically transforming the way the world uses computers.Electronic mail (e-mail) made it possible for even casual computerusers to send messages.In its early years the Internet was the domain of researchers,academics, and government officials. In the 1990s Internetsoftware took giant leaps forward in usability. The biggest changescame with the development of the World Wide Web, a vast tractof the Internet with a multimedia landscape incorporatingpictures, sounds, animation, and even video.Web sites designed as first-stop gateways for Internet surfers arecalled portals. These are often associated with search engines.
THE INTERNET CULTUREToday, all kinds of people are signing onto the Internet in recordnumbers. They use it to communicate with each other, do research,download music, shop, study, browse, and publish their own work.Many companies now have intranets – private organizationalnetworks based on Internet technology. Intranets allow people totransmit, share, and store information within an enterprise. Severalcompanies are marketing stripped-down computers designed tofunction mainly as network terminals, often called networkcomputers or information appliances. These allow people toconnect to the Internet without needing a full-blown personalcomputer
Explanations: Clarifying TechnologyApplicationsMany people define computer literacy as the ability to usecomputers. Application programs, also known simply asapplications, are the software tools that allow a computer to beused for specific purposes:Word processing and desktop publishing: Word processing skill iscritical for anyone who communicates in writing. It’s by far theapplication used most by students. Desktop publishing uses thepersonal computer to transform written words into polished,visually exciting publications.Spreadsheets and other number-crunching applications: Inbusiness the electronic spreadsheet is the personal computerapplication that pays the rent, or at least calculates it.Databases for information storage and retrieval: If wordprocessors and spreadsheets are the most popular PCapplications, databases reign supreme in the world ofmainframes.
Databases for information storage and retrieval: If wordprocessors and spreadsheets are the most popular PCapplications, databases reign supreme in the world ofmainframes.• Computer graphics: Computers are able to produce all kinds ofgraphics, from the charts and graphs produced by spreadsheetsto realistic 3-D animation.• Multimedia and hypermedia: Multimedia tools for PCs make itpossible to combine audio and video with traditional text andgraphics, adding new dimensions to computer communication.Hypermedia tools focus on the interactive capabilities ofcomputers, allowing users to explore a variety of paths throughinformation sources.
• Telecommunication and networking: Every day morecomputers are connected — networked — so they cansend information back and forth; we’re entering an erawhen networking is the norm. Many experts believe thattelecommunication—long-distance communication—willbethe single most important function of computers in thenot-too-distant future.• Artificial intelligence: Artificial intelligence is thebranch of computer science that explores usingcomputers in tasks that require intelligence,imagination, and insight—tasks that have traditionallybeen performed by people rather than machines.• General problem solving: People use computers to solveproblems. Programming languages aren’t applications;they’re tools that allow you to build and customize
Implications: Social and Ethical IssuesThe immediate potential risks of the computer revolutionare:The threat to personal privacy posed by large databasesThe hazards of high-tech crime and the difficulty ofkeeping data secureThe difficulty of defining and protecting intellectualpropertyThe risks of failure of computer systemsThe threat of automation and the dehumanisation ofworkThe abuse of information as a tool of political andeconomic powerThe dangers of dependence on complex technology
The longer-term potential risks of the computerrevolution include:The death of privacyThe blurring of realityThe evolution of intelligence
The four basic hardware components of every computer systemare described below.1. Input devices accept input from the outside world. The mostcommon input device is the keyboard. Other input devices includepointing devices like a mouse and joysticks.2. Output devices send information to the outside world. Mostcomputers use a TV-like video monitor as their main outputdevice and some kind of printer for producing paper printouts.3. A processor, or central processing unit (CPU), processesinformation, performing all the necessary arithmetic calculationsand making basic decisions based on information values.4. Storage devices and memory are used to store information.The most common storage devices are disk drives and tape drives.Different types of memory are used for different long-term andshort-term storage tasks.
Bits, Bytes, and BuzzwordsByte: a grouping of 8 bits.K (kilobyte) (someatimes called KB): about 1000 bytesof information.MB (megabyte) (sometimes called meg):approximately 1000 K, or 1 million bytes.GB (gigabyte) (sometimes called gig): approximately1000 megabytes.TB (terabyte): approximately 1 million megabytes.
THE COMPUTERS CORE : THE CPU AND MEMORYThe CPU : The Real ComputerA modern CPU is an extraordinarily complexcollection of electronic circuits When all of thosecircuits are built into a single silicon chip, as theyare in most computers today, that chip is referred toas a microprocessor. In a typical desktop computer,the CPU is housed along with other chips andelectronic components on a circuit board.Compatibility. Not all software is compatible withevery CPU; that is, software written for oneprocessor may not work with another.
Speed. A computer’s speed is determined in part bythe speed of its internal clock—the timing device thatproduces electrical pulses to synchronize thecomputer’s operations. Computers are often describedin terms of their clock speeds, measured in unitscalled megahertz. Speed is also determined by thearchitecture of the processor—the design thatdetermines how individual components of the CPU areput together on the chip.Parallel processing puts more than one processor ina computer.
The Computer’s MemoryRAM (random access memory) is the most common type ofprimary storage, or computer memory. RAM chips containcircuits that can be used to store program instructions anddata temporarily. You can store a piece of information in anyRAM location—you can pick one at random—and thecomputer can, if so instructed, quickly retrieve it.RAM is called volatile memory because information storedthere is not held permanently.The computer also has nonvolatile memory called ROM(read-only memory) because the computer can only readinformation from it; it can never write any new informationon it. ROM isn’t always hidden away on chips inside thecomputer’s chassis. Many home video game machines andhome computers use removable ROM cartridges aspermanent storage devices for games and other programs.
Buses, Ports, and PeripheralsInformation travels between a computer’s componentsthrough groups of wires called buses. Buses typicallyhave 8, 16, or 32 wires; a bus with 16 wires is called a16-bit bus because it can transmit 16 bits ofinformation at once—twice as many as an 8-bit bus.Some buses connect to expansion slots inside thecomputer’s housing. Users can customize theircomputers by inserting special-purpose circuit boards(usually called cards or just boards) into these slots.
Reading ToolsOptical-mark readers use reflected light todetermine the location of pencil marks onstandardized test answer sheets and similar forms.• Bar-code readers use light to read universalproduct codes (UPCs), inventory codes, and othercodes created out of patterns of variable-width bars.• Magnetic-ink character readers read those odd-shaped numbers printed with magnetic ink onchecks.• In many stores bar-code readers are attached topoint-of-sale (POS) terminals. These terminalssend information scanned by the wand to amainframe computer.
Digitizing the Real WorldA scanner is an input device that can make a digital representationof any printed image.• A digital camera can be used to capture snapshots of the realworld as digital images.• Audio digitizers contain circuitry to digitize sounds frommicrophones and other audio devices.• A video digitizer is a collection of circuits that can capture inputfrom a video source and convert it to a digital signal that can bestored in memory and displayed on computer screens.Sensing devices designed to monitor temperature, humidity,pressure, and other physical quantities provide data used inrobotics, environmental climate control, weather forecasting,medical monitoring, biofeedback, scientific research, and hundredsof other applications.
STORAGE DEVICES: INPUT MEETS OUTPUTTape drives are common storage devices on most mainframe computersand some personal computers. The reason for the widespread use ofmagnetic tape as a storage medium is because a typical magnetic tape canstore massive amounts of information in a small space at a relatively lowcost. Magnetic tape has one clear limitation: Tape is a sequential accessmedium. Because retrieving information from the middle of a tape is time-consuming, magnetic tape is used today mostly for backup of data and a fewother operations that aren’t time sensitive.
Magnetic DisksThe magnetic disk is a readily available alternative to tape as astorage medium: A computer’s disk drive can rapidly retrieveinformation from any part of a magnetic disk without regard to theorder in which the information was recorded.A diskette (or floppy disk) is a small, magnetically sensitive,flexible plastic wafer housed in a plastic case, used to transferinformation between machines and for packaging commercialsoftware.A hard disk is a rigid, magnetically sensitive disk that spins rapidlyand continuously inside the computer chassis or in a separate boxconnected to the computer housing; the user never removes this typeof hard disk.There are several choices of removable media to fill the gap betweenlow-capacity, slow diskettes and nonremovable, fast hard drives:
Optical DisksFor multimedia applications, optical disks provide a storagealternative to hard disks.An optical disk drive uses laser beams rather than magnets to readand write bits of information on the disk surface. While they currentlyaren’t as fast as hard disks, optical disks have considerably more roomfor storing data.CD-ROM (compact disc—read-only memory) drives are opticaldrives capable of reading CD-ROMs—data disks that are physicallyidentical to musical compact discs. Because CD-ROMs are read-onlydevices, they can’t be used as secondary storage devices. CD-RW(compact disc rewritable) drives can write, erase, and rewrite CDs.DVD-ROMs (digital versatile disk-read-only memory) willprobably replace CD-ROMs for multimedia applications because oftheir enormous capacity.
Solid-State Storage DevicesFlash memory is a type of erasable memory chip thatcan serve as a reliable, low-energy, quiet, compactalternative to disk storage. Most experts believe thatsolid state storage technology like flash memory willeventually replace disk and tape storage.