The Information-Processing MachineLike the Analytical Engine, the computer is a machine that changesinformation from one form to another. All computers take in information(input) and give out information (output).The computer’s flexibility isn’t hidden in hardware—the physical partsof the computer system. The secret is software, or programs—theinstructions that tell the hardware what to do to transform the input data(information in a form that it can read) into the necessary output.Evolution and AccelerationComputer hardware evolved rapidly, with new technologies replacing oldevery 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 technologies resultedin computer systems that were more reliable, smaller, faster, moreefficient, and cheaper.Moore’s Law in 1965 predicted that the power of a silicon chip of thesame size would double about every 18 months; this prediction hasbeen 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, and schools.Mainframes and SupercomputersBefore the microcomputer revolution, most information processing wasdone on mainframe computers—room-sized machines with price tagsthat matched their size. Today, large organizations still use mainframesfor big computing jobs.Travel agents and bank tellers communicate with a mainframe using acomputer terminal—a combination keyboard and screen that transfersinformation to and from the computer. Mainframe computers are capableof communicating with several users simultaneously through a techniquecalled 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 the computingpower of a minicomputer at a fraction of the cost. Workstations arewidely used by scientists, engineers, Wall Street analysts, animators,and others whose work involves intensive computation. Personalcomputers are less powerful and less expensive than workstations, butthe line between the two categories is growing blurry.
Portable ComputersToday, one of the fastest growing segments of the PC market involvesmachines that aren’t tied to the desktop—portable computers.Portability is a relative term.Flat-screen, battery-powered laptop computers are light enough to reston your lap while you work or carry like a small briefcase when closed.Embedded Computers and Special-Purpose ComputersNot all computers are general-purpose machines. Many are special-purpose (dedicated) computers that perform specific tasks, rangingfrom controlling the temperature and humidity in a high-rise officebuilding 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 a varietyof 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. Ifcurrent trends continue, we’ll look back on the 1990s as the end ofthe personal computing era and the beginning of the interpersonalcomputing era.The Emergence of NetworksThe first computers were large, expensive, self-contained machinesthat could process only one job at a time. The invention oftimesharing in the 1960s allowed multiple users to connect to asingle mainframe computer through individual terminals. Whenpersonal computers started replacing terminals, they were oftenlinked together in local area networks 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 would becomethe Internet—the global collection of networks that is radicallytransforming the way the world uses computers. Electronic mail (e-mail) made it possible for even casual computer users to sendmessages.In its early years the Internet was the domain of researchers,academics, and government officials. In the 1990s Internet softwaretook giant leaps forward in usability. The biggest changes came withthe development of the World Wide Web, a vast tract of the Internetwith a multimedia landscape incorporating pictures, 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. Manycompanies now have intranets – private organizational networks basedon Internet technology. Intranets allow people to transmit, share, andstore information within an enterprise. Several companies are marketingstripped-down computers designed to function mainly as networkterminals, often called network computers or information appliances.These allow people to connect to the Internet without needing a full-blown personal computer
Explanations: Clarifying TechnologyApplicationsMany people define computer literacy as the ability to use computers.Application programs, also known simply as applications, are thesoftware tools that allow a computer to be used 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, visuallyexciting publications.Spreadsheets and other number-crunching applications: In businessthe electronic spreadsheet is the personal computer application thatpays the rent, or at least calculates it.Databases for information storage and retrieval: If word processorsand spreadsheets are the most popular PC applications, databasesreign supreme in the world of mainframes.
Databases for information storage and retrieval: If word processorsand spreadsheets are the most popular PC applications, databasesreign supreme in the world of mainframes.• Computer graphics: Computers are able to produce all kinds ofgraphics, from the charts and graphs produced by spreadsheets torealistic 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 of computers,allowing users to explore a variety of paths through informationsources.
• 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—will bethe single most important function of computers in the not-too-distant future.• Artificial intelligence: Artificial intelligence is the branch ofcomputer science that explores using computers in tasksthat require intelligence, imagination, and insight—tasksthat have traditionally been performed by people rather thanmachines.• General problem solving: People use computers to solveproblems. Programming languages aren’t applications;they’re tools that allow you to build and customizeapplications.
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 of keepingdata secureThe difficulty of defining and protecting intellectual propertyThe risks of failure of computer systemsThe threat of automation and the dehumanisation of workThe abuse of information as a tool of political and economicpowerThe 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
END OF CH3
CH 4 COMPUTER HARDWARE
The four basic hardware components of every computer system aredescribed 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 output deviceand some kind of printer for producing paper printouts.3. A processor, or central processing unit (CPU), processesinformation, performing all the necessary arithmetic calculations andmaking basic decisions based on information values.4. Storage devices and memory are used to store information. Themost common storage devices are disk drives and tape drives.Different types of memory are used for different long-term and short-term storage tasks.
Bits, Bytes, and BuzzwordsByte: a grouping of 8 bits.K (kilobyte) (someatimes called KB): about 1000 bytes ofinformation.MB (megabyte) (sometimes called meg): approximately1000 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 complex collectionof electronic circuits When all of those circuits are builtinto a single silicon chip, as they are in mostcomputers today, that chip is referred to as amicroprocessor. In a typical desktop computer, theCPU is housed along with other chips and electroniccomponents on a circuit board.Compatibility. Not all software is compatible withevery CPU; that is, software written for one processormay not work with another.
Speed. A computer’s speed is determined in part by thespeed of its internal clock—the timing device thatproduces electrical pulses to synchronize the computer’soperations. Computers are often described in terms oftheir clock speeds, measured in units called megahertz.Speed is also determined by the architecture of theprocessor—the design that determines how individualcomponents of the CPU are put together on the chip.Parallel processing puts more than one processor in acomputer.
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 and datatemporarily. You can store a piece of information in any RAMlocation—you can pick one at random—and the computer can, ifso 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 read informationfrom it; it can never write any new information on it. ROM isn’talways hidden away on chips inside the computer’s chassis.Many home video game machines and home computers useremovable ROM cartridges as permanent storage devices forgames 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 of informationat 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 to determinethe location of pencil marks on standardized testanswer sheets and similar forms.• Bar-code readers use light to read universal productcodes (UPCs), inventory codes, and other codescreated out of patterns of variable-width bars.• Magnetic-ink character readers read those odd-shaped numbers printed with magnetic ink on checks.• In many stores bar-code readers are attached topoint-of-sale (POS) terminals. These terminals sendinformation scanned by the wand to a mainframecomputer.
Digitizing the Real WorldA scanner is an input device that can make a digital representation ofany printed image.• A digital camera can be used to capture snapshots of the real worldas digital images.• Audio digitizers contain circuitry to digitize sounds from microphonesand other audio devices.• A video digitizer is a collection of circuits that can capture input froma video source and convert it to a digital signal that can be stored inmemory and displayed on computer screens.Sensing devices designed to monitor temperature, humidity, pressure,and other physical quantities provide data used in robotics,environmental climate control, weather forecasting, medical monitoring,biofeedback, scientific research, and hundreds of other applications.
STORAGE DEVICES: INPUT MEETS OUTPUTTape drives are common storage devices on most mainframe computers andsome personal computers. The reason for the widespread use of magnetictape as a storage medium is because a typical magnetic tape can storemassive amounts of information in a small space at a relatively low cost.Magnetic tape has one clear limitation: Tape is a sequential access medium.Because retrieving information from the middle of a tape is time-consuming,magnetic tape is used today mostly for backup of data and a few otheroperations that aren’t time sensitive.
Magnetic DisksThe magnetic disk is a readily available alternative to tape as a storagemedium: A computer’s disk drive can rapidly retrieve information fromany part of a magnetic disk without regard to the order in which theinformation was recorded.A diskette (or floppy disk) is a small, magnetically sensitive, flexibleplastic wafer housed in a plastic case, used to transfer informationbetween machines and for packaging commercial software.A hard disk is a rigid, magnetically sensitive disk that spins rapidly andcontinuously inside the computer chassis or in a separate box connectedto the computer housing; the user never removes this type of 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 storage alternativeto hard disks.An optical disk drive uses laser beams rather than magnets to read andwrite bits of information on the disk surface. While they currently aren’t asfast as hard disks, optical disks have considerably more room for storingdata.CD-ROM (compact disc—read-only memory) drives are optical drivescapable of reading CD-ROMs—data disks that are physically identical tomusical compact discs. Because CD-ROMs are read-only devices, theycan’t be used as secondary storage devices. CD-RW (compact discrewritable) drives can write, erase, and rewrite CDs. DVD-ROMs (digitalversatile disk-read-only memory) will probably replace CD-ROMs formultimedia applications because of their 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.