Definition and History of Computer and Internet

8/12/2019 Definition and History of Computer and Internet

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continuous way. This response is an analog of the process embodied in the problem it is working on. Ageneral%purpose analog computer is equipped with resistors, capacitors, and inductors that can beinterconnected to represent the conditions of a problem. 9igital computers, on the other hand, changethe values of numbers 'more specifically, binary digits, or bits( that represent the components of theproblem being computed. The numbers in a digital computer can be used to represent other symbols as

well, such as letters, plus and minus signs, and so on. 9igital computers,computers, work in finite steps. :ybrid computers 'see below(, as the name implies, combine featuresof the two main types.

Analog Computers. Analog computers come in a variety of forms. A common analog computer is theautomatic transmission of an automobile. 7t &computes& the linkage between the engine and the driveshaft by using pressure differences on fluids within the transmission to control the shifting of the gears."oving the shift lever or changing the speed of the car causes the computer to change its internalmechanical state. "ost mechanical analog computers are relatively large, but there are also microchipanalog computers. These computers use tiny mechanical elements, such as rods and springs, etched inwafers of silicon by techniques similar to those used for the microelectronic chips in digital computers

'see below(.

Analog computers are &programmed& by setting up the physical characteristics of the computercomponents. 7n scientific computers this is usually done by switching components into or out ofcircuits, interconnecting components by patch cords, and changing the settings of variable resistors,capacitors, and inductors in the circuits. 7n an automobile transmission the program is changed bymoving the gear shift lever, causing the fluids in the transmission to take different paths and producedifferent results.

Except for production items such as automatic transmissions and music synthesi;ers, analog computerstend to be tailored to the particular computational task at hand. There are few large general%purposeanalog computers.

Digital Computers. Almost all digital computers are electronic. All have somewhat similarcomponents for accepting, sorting, manipulating, and transmitting information, and all make use of arelatively small number of basic functions to perform their tasks. The most important characteristics ofdigital computers are speed, ability to operate in exactly repeatable ways, and flexibility. ecause ofthese characteristics, digital computers can be used in an enormous variety of applications, fromrunning a wristwatch to guiding a spacecraft.

There are our main categories o !igital computer"

supercomputers, mainframe computers, minicomputers, and microcomputers. 'A personalcomputer can be thought of as a general%purpose microcomputer.( All digital computers share the samegeneral design characteristics, but differ in si;e and computing speed, or both.

Personal Computers.


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7n general, a personal computer has a single microprocessor chip as its central processor unit 'seebelow(.


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unique address or number. An item of information is stored in memory by assigning it an address. Toretrieve the information, the computer &looks& in the cell and copies down the contents in its&headquarters& unit, to be described shortly. The capacity of a single memory cell is called a word. @ora personal computer a word is typically *4 binary digits, or bits, long. An /%bit length is called a byte.Typical mainframe%computer words range from 25 to 46 bits '6 to / bytes( in length, while

minicomputers have word lengths ranging from *4 to 25 bits '5 to 6 bytes(. "icrocomputers typicallyuse word lengths of /, *4, or 25 bits '*, 5, or 6 bytes(.

Secon!ar$ memor$ is usually located outside the main part of the computer. ecause secondarymemory is slower than main memory, it is used mostly to store informationnot immediately needed bythe computer. To use secondary memory, the headquarters unit of the computer usually transfers thecontents of part of the secondary memory to themain memory. "ain memory is expensive, socomputer designers store as much information as possible in secondary memory.

Central Processor Unit.The core pair ofsubsystems of a computer consists of the control unit 'C0(and the arithmetic and logic unit 'A?0(. Together, these make up the central processor unit, or C


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usually at least two sets of registers in a computer8 one set for the use of the C71C has fewerinstructions but is faster. >71C processors may be superior where large numbers of relatively simplecalculations are required, as in graphics%intensive applications$ C71C processors may have the edge in

general%purpose applications.

@or both C71C and >71C processors the time is coming when the computing speed will be limited byneed to run everything through the single 1ome new supercomputers, such as the connection machine,solve this problem by using arrays of von Beumann microprocessors. Connection machines are usedwhere large amounts of similar data are to be processed, as in weather forecasting and high%resolutiongraphics. A parallel machine distributes the data among its processors and performs the calculationstogether. Beural network computers, another form of parallel processors architecture, use very simplemicroprocessors. Each microprocessor acts like a neuron, responding to signals from several differentinputs. The computer comprises a highly interconnected network of these microprocessors. Beuralnetwork computers can be taught$ as new data come in, they ad!ust the responses of individualmicroprocessors andor change the interconnectionpaths. Beural computers are not programmed by means of algorithms such as those used by other ofdigital computers$ rather, the connections, the response algorithms, and the training laws are specifiedby the programmer.

&nternal Communications. A computer must have a central communications path connecting all themain subsystems. 7n many computers this channel is called the bus. "any mini% and microcomputersystems incorporate a general%purpose bus that can connect a variety of special%purpose functions tothe computer. #ith such a bus, a computer can be altered piecemeal to meet demand or as thetechnology changes.

&nput an! Output.The purpose of the input function of the computer is to convert information fromthe external world%%that is, images, sounds, keystrokes, pointer positions, thermocouple voltages, andso on%%to binary digits.

The output function, by a reverse process, converts binary digits to visual displays, printed characters,sounds, control voltages, and the like. asically, anything measurable, and that can be converted intoan electrical analog of binary digits, can be used by a computer. Anything a computer can compute can,in turn, be converted into a form understandable by humans or by other machines. Dne frequently used


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inputoutput consists of two elements8 an analog%to%digital converter and a digital%to%analog converter.The first converts voltages, such as those used in an analog computer, to binary digits$ thesecond converts binary digits to voltages.

T#E '&(ARY (UM'ER SYSTEM

All digital computers are basically collections of switches. Each switch has two possible positions8open, &-&, or off$ and closed, &*&, or on. The two positions form the basis of the binary 'or two%valued8-, *( number system. Dtherwise, the computer uses numbers as we do in the familiar decimal system.

'inar$ (um%ers.Any number can be represented in binary as well as in decimal form.@or example,the number *,+/ expressed in binary form is *****-----*. As is the case with decimal numbers, wecan interpret a binary number as the sum of a series of powers of the base number. @or example, indecimal notation8*,+/ * F *-2 G + F *-5 G / F *-* G F *--that is,*,+/ * F *,--- G + F *-- G /F *- G F *.1imilarly, in binary notation8*****-----**F5*- G*F5+G*F5/G*F5G*F5 4G- F 5 G -F 56 G - F 5

2 G - F 55 G - F 5* G * F 5 -or, in decimal notation8*****-----* * F *,-56 G * F *5 G * F 54 G *F *5/ G* F 46 G - F 25 G - F *4 G - F / G - F 5 G * F *

Bumbers can be used to represent nonnumerical quantities, such as letters of the alphabet andpunctuation marks. A standard code is often used to assign specific patterns of binary numbers toprintable characters.

Logic Circuits.inary numbers can also be used to represent the results of logical operations. @orexample, if * represents T>0E and - represents, we can represent all functions logical 'except&maybe&( by sequences of binary numbers. #e can then arrange the circuits of a computer to makelogical tests on statements given to the machine. These logic circuits enable the C(, produces a * at its output only if oneinput but not the other is a *. 7n other words, an AB9 gate produces -=s unless both inputs are *=s$ anD> gate produces -=s only if both inputs are -$ an HD> gate demands one of each.


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To see how this works, suppose a computer is in charge of baking a roast in a microwave oven. Theowner of the oven programs it to stop cooking the roast when either the preset time has elapsed or thethermometer in the roast reads *6-I@. The logic gate used by the computer in the oven for this task isan D> gate. At the start of the cooking process, neither the timer output nor the thermometer outputsatisfies the conditions set in the oven 'timer output greater than or equal to 2- minutes, thermometer

output greater than or equal to *6-(. Therefore, the D> gate will produce a - at its output, since bothinputs are -. At some point one or both of the conditions will be met and the D> gate will produce a *,thereby shutting down the oven.

Bow suppose the chef, knowing it is possible to get a thermometer reading that is toohigh if thethermometer is touching the bone in the roast, sets the oven to stop cooking when the thermometer hasat least reached a certain point and the proper cooking time has elapsed. The difference between thisand the previous situation is that an AB9 gate is used in the microwave computer8 the gate producesrequired * only when both the temperature has reached *6-I@. and the roast has cooked for 2- minutes.All the complex logical operations of much more sophisticated computers can be reduced tocombinations of logic%gate operations much like those described.

COMPUTER #ARD)ARE

The descriptions to follow will generally apply to both larger computers and personal computers. 7nsome cases comments appropriate to one or other class will be made.

Electronic !igital computersconsist of two main types of circuit8 logic gates and memory circuits. Dfcourse, a computer also contains other types of circuit, such as drivers, buffers, and oscillators. ut thegates and flip%flops 'see below( perform the key logical functions of the computer. The gate circuitproduces its desired output only while the input signals are present$ when the input signal stops, theoutput of the gate reverts to its ;ero input condition%%it has no memory. '1ee section ?ogic Circuits inThe inary Bumber 1ystem.(

Flip*lopsare the key elements of memory circuits. A flip%flop is so called because its output voltageflips from one value to another and stays there until it an input signal to change 'flop( back. The mostfamiliar, everyday example of a flip%flop is a light switch. 1uppose the light is off. #hen you push thebutton, the switch closes and the light goes on.


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The thir! generation of digital computers began with the introduction of the multiple form of thetransistor8 the integrated circuit. An integrated circuit crams as many circuit elements on a chip ofsubstrate%%generally silicon%%as is possible. 7ntegrated circuits of the mid%*+4-=s contained four or fivelogic gates each. 7n the early *+-=s the first ?17 'large scale integrated( circuits began to appear. 7n the*+/-=s the emphasis was on )?17 and ):17 'very large scale integrated and very high speed

integrated( circuits. 7n *++* 7ntel produced a chip, the i/4-H


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chips hold *" to *4" bits each '*" *,-6/,4 bits(. Eight or nine 6" chips constituted the mainmemory of many mid%level *++5 personal computers$ this amount of memory is the equivalent ofabout 4-,--- words, or about *,/-- printed pages, of simple English. >A"s are reliable and may runfor years, performing billions of operations. >A"s remember only what you told them last$ everythingelse is erased. >A"s are relatively low consumers of power, comparable to other 7Cs of roughly equal

si;e and packing density. 1ome >A"s consume so little power that a small battery can be used to keepthem retentive, if not active, after the main power has been turned off. These >A"s are often used insmall portable computers and calculators.

>A"s lose all memory when power is off. >D"s, on the other hand, remember virtually forever.1ome >D"s are used for tasks that entail following the same set of instructions over and over again.>D"s are generally slower than >A"s, but have the advantage of a permanent internal memory."oreover, what >D"s lack in speed of response they make up in packing density$ >D"s haveroughly twice the memory capacity of >A"s.

The random%access feature of both >D"s and >A"s refers to the ability of the microprocessor or

other CA" or >D" and the CD"(, or by other means, as in some of the newer erasablewritable memory chips.

E,ternal Memories.External, or secondary, memories include magnetic tapes, magnetic disks, opticaldisks, and magnetic bubbles. External memories are cheaper than internal3usually semiconductor%based%%memories. 7n addition, most external memories can be moved from one computer to another.The ma!or drawback of secondary memories is that they are slower than internal memories.

Magnetic tapes in the form of cassettes for car or home stereos and videotape cassettes are familiartypes of external memory. oth store analog data, that is, signals that vary continuously%%for example,from a violin=s pianissimo to the blast of a rock group. To use these media for computers requires thatthe form of the data be changed to digital, that is, to signals that vary only between two prescribedvalues, corresponding to the binary digits - and *. They are by far the least expensive medium and alsoby far the slowest. ?arge computers, on the other hand, use high%speed multitrack magnetic tapes tostore large quantities of data. These tapes are commonly used to copy all the information from thecomputer system=s disks 'see below( to serve as a backup.

Tape cartri!gesare similar in appearance to audiotape cassettes but are designed for digital recording.They record at higher densities than audiotape cassettes and use specially tested tapes. They are used asbackups for hard%disk systems. )ideotapes increase the speed of access, but at a higher cost. 1omevideo recorders may serve as backup storage devices for hard disks. 9igital audio tapes '9AT( are alsoused as a backup medium. A digital audio tape can hold up to a billion bytes of data in a cassettesmaller than an audiotape cassette. All types of tape storage have one ma!or drawback. They are serial$


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the tape must be run through to get to a required item. This is a time%consuming process. The questionof time brings us to the second most popular storage medium for smaller computers, the floppy disk.

The lopp$ !is-is the logical compromise between the magnetic tape and the phonograph record. 7tconsists of a thin, flexible '&floppy&( disk of plastic coated on one or both sides with magnetic material.

The coated disk is encased in a protective envelope or shell that contains holes for access by thereadrecord head and the disk%drive motor.

@loppy disks are played like a phonograph record, but with a magnetic recorder head rather than aneedle. ?ike a magnetic tape, a floppy disk can form a permanent record of a program or data$ becauseit is erasable, its content can be altered.

The floppy disk, unlike magnetic tape, is a random%access medium. The information recorded on afloppy disk is laid out in concentric circles 'tracks( on its surface. Dne or two of the tracks aregenerally used to store a table of contents. To find a particular record on the disk, the computer tells themagnetic head to move to the track with the table of contents and find the location coordinates of the

desired information. The computer does this by reading the data on the track as the disk spins by themagnetic head. Dnce the desired record is located, the computer tells the magnetic head to move to thatspot. The same concepts hold for recording information. To change information on a tape, the entiretape must be read out, the changes inserted, and the revised version rerecorded. A floppy%disk systemsimply revises a specific segment of itsrecords, leaving the rest of the surface unaltered. This isbecause a given record can be recorded in pieces, with each piece stuffed into whatever location isconvenient. The only additional requirement is that the table of contents on the disk changed to tallywith the changes made on the disk.

7n the 0nited 1tates floppy disks are manufactured in two main si;es8 2J inches and K inches '+ and*2 cm(. A typical single floppy disk can store from about 24,--- to *,66-,--- characters 'bytes(,equivalent to 5-- to /- double%spaced pages of typed text. @loppy disk drives are built into mostpersonal computers and cost about L*-- or less to replace. lank floppy disks cost from L* to L2 each.

A hard disk is much like a floppy disk. The main difference is that the hard disk is of metal. A hard diskis therefore more rigid, can be spun faster, and packs more information than a floppy disk. A typicalpersonal computer hard%disk drive is about the si;e of a floppy%disk drive and holds between 5-million and 5- million or more characters, compared with *.66 million characters for a high%density2J%inch diameter floppy disk. Also, hard disks have much higher communication rates with theircomputer than either floppies or audiotape cassettes. A search that might take minutes on an audiocassette, or up to a few seconds on a floppy, would take hundredths of a second on a hard disk. Thehard disk is the external storage medium of choice for current records and applications software onmost computers.

"any hard disks are permanently enclosed in an airtight, dustproof housing. 7f such a disk fails, thecomputer is useless without a backup memory. 1ome hard disks can be removed from their drives, ascan floppy disks. >emovable hard disks have less storage than fixed disks of comparable development.:ard disks cost more than floppy disks$ however, they tend to cost less per unit of capacity.


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The optical disk, detailed in this illustraton, is similar to both the magnetic disk and the phonographrecord. There are three main types of optical disk8 C9%>D" 'compact disk read%only memory( disks,#D>" 'write once, read mostly( disks, and erasable optical disks. C9%>D" disks and #D>" disksare used to store large amounts of information that does not change. #D>" disks can be written ononce only$ once entered, the information cannot be erased. Erasable optical disks can be used like hard

disks. Dptical disks range in si;e from those to videodisks to the disks of diameter K inches '*2.2cm(, 6.5 inches '*5 cm(, and smaller used for audio compact disks. '1ee also )ideo >ecording and>eproduction.(

An optical disk, like a phonograph record, stores information on a spiral track. As is the case withmagnetic disks, the optical%disk player pickup head moves radially back and forth along a fixed trackrather than on a pivoted arm. An optical disk uses a laser beam to store and &read& its information.

7n a phonograph record the information is stored as undulations in the grooves of the record. Theseundulations are converted by the needle and tiny magnets to electrical signals that are fed to anamplifier. The surface layer of a magnetic disk has varying intensities of magneti;ation$ the magnetic

field is detected by a small electromagnet in the pickup head and converted to electrical signals. Thesurface of an optical disk contains information in the form of little pits, corresponding to binary digits.The variations in intensity of the laser light reflected from the pits are detected by a photocell thatconverts them into electrical signals. Erasable optical disks are coated with a material that changes itsoptical polari;ation in response to a magnetic field from the write head of the disk drive. Thesechanges can then be converted into electrical signals by the read head. The magneto%optical disk iserased by the combined effect of a magnetic field and a laser beam.

A CD*ROM !is-of diameter 6.5 inches '*5 cm( can hold the equivalent of about 2--,--- pages ofprinted material, or 4-- million characters 'bytes( ofinformation, at a production cost of less than Lper disk, although retail prices in *++* varied from about L- to several hundred dollars. CommercialC9%>D"s are used to distribute a wide variety of reference works, clip%art images for computergraphics, animation, and combinations of text and audio and video materials. They are becomingindispensable in multimedia computing. "agneto%optical disks come in diameters of K and 2J inchesand hold from *5/ million to 4- million characters each.

A *5%inch '2-%cm( optical disk can hold *. billion characters of digital data%%more than a thousandtimes as much as an /%inch '5-%cm( floppy disk. A6%inch '*-%cm( disk can store the equivalent of about 5- million characters per side.

A form of magnetic recording called perpendicular or vertical recording promises to keep floppy disksin the running for storing large amounts of information.


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&nputOutput E/uipment.A computer must be able to communicate with the outside world. 7naddition to the external memory units reviewed above, a computer may be required to communicatewith its operators, with telecommunications lines, and with sensors, actuators, or other machines.

ComputerOperator &nterace.Communicating with a computer is not like talking to a person.7ndeed, it is more like talking to a typewriter. 7n many ways this is not as satisfying as a normalconversation. This situation results partly from hardware deficiencies, but more from softwareinadequacies%%we do not know, for example, how people think, much less how to program a computerto simulate thinking in more than very simple ways.

The most common machinehuman interface device for a computer is a T)%like display and atypewriter%like keyboard. The display is called a C>T 'cathode ray tube( terminal or a video displaytube ')9T(. 9isplays used in industry cost from L5- to several thousand dollars.


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Dther means of personcomputer interfacing include &!oysticks& for conveying positional informationregarding a display on a C>T or T) screen, &mice& 'hand%held devices( for performing the same task,and pointers for picking out specific spots on a display screen or plotting board. @or some C>Tdisplays a finger can be used as the pointer.

Telecommunications &nter*aces.?inked to a telecommunications system, the personal computer cantalk to other computers similarly connected. The gadget that performs this function via an ordinarytelephone line is called a modem 'modulator%demodulator(. Contemporary modems are of two types.Dne is an external box that connects to the telephone line and the computer. The other is a circuit boardthat fits inside the computer. The @ederal Communications Commission and many state public utilitycommissions have rules against the use of unauthori;ed interconnection devices$ all commerciallyavailable modems meet these requirements. The advantage of such a modem is that the computer isprogrammed to dial telephone numbers automatically. "odem transmission speeds range from *5- tomore than *,5-- characters per second.

7nternational standards govern modem speeds, signaling speeds, and data compression techniques.

Consequently, it is possible to send computer data between most points in the world with relative ease.1ince the late *+-=s a number of other telecommunications systems, designed specifically for use withall sorts of computers, have come on the market. These systems are known as local area networks, or?ABs. They form the core technology of many schemes for office automation. Dffice automation is ama!or area of computer applications, concentrating on the uses of computers,particularlymicrocomputers, coupled with advanced telecommunications systems, to help facilitate theflow of information. '1ee also usiness "achinesand Equipment.(

SensorActuator &nteraces. A ma!or early use of computers was in controlling machine tools."inicomputers connected to large lathes, milling machines, and other production machinery couldmonitor the machine operations and alter them to produce a perfectly machined piece each time. Thecomputer is equipped with sensors that provide it with information on the position of the various partsof the machine, such as the cutting head, and of the part that is being machined. The computercompares the sensor data with its preprogrammed instructions and generates commands to actuators tomove the machine parts to conform to the preestablished pattern. Computers are frequently used toreplace people in ha;ardous tasks, such as the handling of radioactive materials. '1ee also "achineTools$>obot.(

Personal computerscan control many things in the home, such as energy consumption, sprinklersystems, and security systems, provided they have the proper sensors 'of temperature and sunlight, soilmoisture, burglars, and so on(. The trouble is that such systems are expensive. 0ntil integrated circuitsare built into many types of appliance there will not be strong economic arguments for the use ofpersonal computers for sensing and control.

The ma!or automobile manufacturers are turning to the use of integrated circuits and microprocessorsin automobile control systems%%mainly in response toair%pollution and fuel%economy regulations. "any types of sensor are being developed for thisindustry$ similar devices will then be available for the personal computer.


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Fith*0eneration Computers.The advent in the *+/-=s of massively parallel and neural networkcomputers signaled the first results of a conceptual revolution. Dne of the key concepts is that ofknowledge processing. Nnowledge processing involves the development of computer &reasoning,&coupled with access to information as to how experts approach problem solving. A typical fifth%

generation computer will, in effect, be an electronic expert in a particular area. The user willcommunicate with these computers in a natural language rather than in the styli;ed codes used bytoday=s systems.

The 0nited 1tates and apan are the front%runners in the race to produce the next generation ofcomputers. '1ee also Artificial 7ntelligence 'A7(.(

COMPUTER SOFT)ARE

Sot1are is the computer=s instructions. 7ncluded in this definition are programs, program subsectionsor routines, and data. Thus, software tells the computer what to do, how to do it, when to do it, in what

sequence, and how often. Computer software is often known simply as the program.

Computer programsare lists of instructions that tell the computer to do things. Computers have to betold everything. Computer programs are oftenwritten in a form of shorthand. :ere is a program for crossing the street.

O Crossing%the%street program O Approach the curb$ 7@ BDT 'at the corner D> at a pedestrian crossing( T:EB proceed to the corner or the nearest pedestrian crossing$ E?1E 7@ there is a traffic signal at the crossing T:EB wait for the signal to indicate A?N&$ >EE


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you are back at the start($ 7@ you are back at the start T:EB restart the program$ E?1E congratulate yourself on your survival$ >ET0>BOto whatever you were planning to

do nextO

This program is written inPseu!oco!e % understandable by the programmer rather than the computer. The parts that aresurrounded by O and O are ignored by the computer$ they are there to help the programmer. Two keystructural features of programs are the conditional statement8 7@ something is true, T:EB dosomething, E?1E 'otherwise( do something else$ and the loop8 >E


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Assem%l$ language programsprovide the most compact form for accomplishing the desired purpose.They also take longest to write. :igher%level languages, such as C, T>AB, and the like use more memory than assembly languages but are much easier to work with.As memory costs went down in the *+-=s and *+/-=s and programmer costs went up, higher%levellanguages became dominant. The higher%level languages most likely to come to the attention of


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selected may cause another set of alternatives to be displayed, one of which is to be selected, and soforth.

1ome menu programs, such as that used to compile and edit the text for this article, have a small set ofcommands that cause the computer to perform various tasks. A sophisticated menu program might start

with relatively long explanations of alternatives, then gradually reduce its message length as theoperator increases in manipulative skill.

A large number of the more traditional applications programs must be written in menu%like or user%oriented formats if public acceptance of personal computers is to increase. As the use of computersspreads, and particularly as schoolchildren learn to use them, a large proportion of the 0nited 1tatespopulation will have been exposed to some form of programming by the turn of the century. Theemphasis in software will be on making the humanmachine interface as transparent, and friendly aspossible. Dne particular aspect of this search is worthy of special notice.

Programmerless Sot1are. The growth of personal computers has greatly accelerated the

development of so%called programmerless software. :ere, the user can interact by means of thecomputer controls with a display showing a logical or visual structure of some kind. The user can keyin other information at any point in the display and then go on to the next point. The structure can beused again and again, with different data each time, if necessary. The user does not have to knowanything about programming to use the program. "any spreadsheet and database programs incorporatethese programmerless features. A primary means of querying large mainframe databases is via 1R?'1tructured Ruery ?anguages$ pronounced sequel(, in which the user asks the database for informationin a syntax much like standard English. 1R? links to personal computer databases have becomepopular.

0raphical User &nteraces 20U&3.As microcomputers and engineering workstations gained in powerduring the *+/-=s computer displays evolved from being character%based to the use of extensive bit%mapped graphics. This development allowed the design of programs3particularly operating systemssoftware including graphics and alarge variety of display methods. "ultiple programs can be screenedand the application programs run 'apparently( simultaneously. The "acintosh series of computersproduced by Apple led the way to the popularity of M07 interfaces for personal computers. #indows'"icrosoft Corporation(, D15


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E!ucation.7n education, some trends seem clear. ecause of the expanding importance of computersthe economic growth of society, people must know how to interact with a computer. "ost people willlikely have to know as much about operating computers as they know about operating anautomobile.

Computers are becoming increasingly useful tools of education. @or some applications, such as routine

instruction, they can be superb ad!uncts to the teacher. They are ideally suited to self%paced instructionwhere the course ob!ectives and content are well defined.


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more 7"%compatible personal computers were manufactured by 7"=s competitors 'for example,Compaq( than by 7" itself. The leading manufacturer of personal computers not compatible with the7"


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#&STORY OF COMPUTER

Twenty years after the #ar of */*5 an English inventor and mathematician, Charles abbage, wascommissioned by the ritish government to develop a system for calculating the rise and fall of thetides. The ritish navy ruled the oceans of the world at that time, and crucial to that control was

accurate knowledge of the tides. Tides are caused by extremely complex gravitational interactionsbetween the earth, the moon, and the sun. The task of accurately charting tidal patterns was beyond thecapabilities of most nations of the world.

'a%%agedecided that the only answer was to build a device he called the analytical engine. yselecting and meshing an array of gears, levers, and counter wheels in a frame resembling anautomobile gearbox gone mad, abbage designed the first programmable computer, complete withpunch cards for data input. The machine could add, subtract, multiply, and and, by means of variouscombinations of its gears and levers, could perform many other types of calculation.

Each cog tooth and each gear wheel 'some -,--- in all( in abbage=s engine had to be built to

extremely fine tolerances. This task was beyond the artisans of his time. Although some smallerversions of abbage=s engine were built and operated successfully, the machine of his dreams wasnever reali;ed in his lifetime. :e died an embittered man.

Dther attempts were made to build mechanical general%purpose computers. All suffered the fate ofabbage=s machine, and for similar reasons. 7t became clear that mechanical methods of general%purpose computing on all but the most modest scale were not practical. The demand for more effectivemeans of calculation grew, but themechanical devices of the *+2-=s were too slow and cumbersome to satisfy the needs of scientists,engineers, and businessmen. This situation was turned around by using electric switches rather thangears to count. 1witches can be made to achieve the same results as abbage=s machine. The onlyconceptual difficulty is that mechanical switches are ordinarily on or off$ one cannot make such aswitch represent a number between one and ten as a counter wheel can. 1witches operate on a binarynumber system$ people count in tens. ut, once familiar with a binary system, people could use aswitch%based computer to perform complicated calculations.

A rela$ computerwas built in Mermany in *+6* by Nonrad use. Called the 2, its logical operationswere alterable by switching among the relays.

7n the 0nited 1tates, 7nternational usiness "achines built a machine at :arvard 0niversity over theyears from *+2+ to *+66. The computer, called the "ark 7 sequence%controlled calculator, was builtunder the direction of :oward Aiken to perform calculations for the "anhattan


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The Electronic Computer.The vacuum tube, an electronic device invented in the early 5-th century,was the basis for the first computer revolution. The vacuum tube was ideal for computers. 7t had nomechanical moving parts, switched at rates far faster than any mechanical device, and was relativelyreliable and long%lived. The first vacuum%tube computer, the Atanasoff%erry Computer 'AC( at 7owa1tate 0niversity, was built at about the same time as the "ark 7. AC marked the beginning of the

computer revolution.

A splendid example of these irst*generation electronic computers was E(&AC 2Electronic(umerical &ntegrator an! Calculator3. EB7AC weighed !ust over 2- tons and took up 2,--- cubicfeet '/ cubic meters( of space. 7ts */,--- vacuum tubes used *6- kilowatts of electric power3enoughfor a medium%si;ed town. 7t was not quite up to the computing capability of, or nearly as flexible as, aL-- personal computer of today.

7n *+* the first assembly%line computer, the U(&4AC 5 2Uni+ersal Automatic Computer36was builtby the >emington >and Corp., later to becomepart of 1perry >and. A 0B7)AC was delivered to theMeneral Electric Company in *+6$ 6 were built in all. 0p to the time of 0B7)AC *, 4- electronic

computers had been built. 0B7)AC * allowed rapid, extensive computing to be applied to onscientificproblems.

The next advance in computer technology was the transistor. 7n *+6 a team of scientists, led by ohnardeen, #alter rattain, and #illiam 1hockley, developed the first transistor at ell Telephone?aboratories. The transistor represented a quantum leap over the vacuum tube%%in the physical as wellas the metaphorical sense. Transistors switch as fast as vacuum tubes, but use much less power and aresmaller. Computers of astounding complexity and speed were now possible. abbage=s dream began toseem tame.

A +acuum tu%eis built by encapsulating a collection of small metal parts. A transistoris composed ofa single slice 'a chip( of a material called a semiconductor. A semiconductor is in general mediocreconductor of electricity$ under certain conditions, however, it can be made to conduct, and evenamplify, electricity. The first transistor was the !unction transistor. This was the famous cat=s whiskerused in the first radio receivers. The !unction transistor was improved in *+*, again at ell ?abs, withthe development of the grown transistor. The 'asic Semicon!uctor Material% germanium or silicon,for example % is melted in a pot. "inute traces of other substances are added to change the electricalcharacteristics of the semiconductor. A small pure cr$stal o the semicon!uctorintroduced into themix acts as a seed for the growth of a large single crystal. #ith this invention, technologists were betterable to control the characteristics of the transistor. The technology for manufacturing transistorssteadily improved until, in *++, the first integrated circuit, the multiple form of the transistor, wasproduced.

&ntegrate!*circuit technolog$ allowed the inclusion of discrete components such as resistors andcapacitors on the chip containing the transistor. Thus the basic logical element, the &flip%flop,& whichrequired two transistors and some resistors and capacitors in the early *+-=s, could be packaged as asingle unit about the si;e of a transistor.

&ntegrate!*circuit technolog$made it possible to !am more and more elements onto a single chip.Entire assemblies of parts could be manufactured in the time previously needed for a single part. The


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cost of providing a particular computing function decreased proportionately. The number ofcomponents per integrated circuit has doubled every year since *+4 and shows no signs of slowing.:owever, metals and semiconductors are composed of molecules, and wires only a few moleculesthick are extremely fragile and difficult to control even with the most advanced technology.

The number of functions that can be crammed onto a single semiconductor chip continues to grow. Asthe number of elements on chip increases, the functions performed by the chip becomes more complex,the speed at which a given function is performed tends to rise, the power required to perform a givenfunction decreases, but the manufacturing cost per chip stays about the same.

A microcircuit is a chip containing perhaps many thousands of separate components. Theconsequences for computing of miniaturi;ation on this scale can be seen from the fact that by *+/2there were some 5 million personal computers in the 0nited 1tates.

Ma,is6 Minis6 an! Micros.The second generation of computers was based on the transistor and lastedabout * years. The third generation began in the mid%*+4-=s and produced the mainframe computer

and the minicomputer.

The mainrame computer is big, requires air conditioning because of its substantial powerconsumption, and needs systems programmers, applications programmers, and operators. A goodexample of the mainframe computer is the 7" 62-- series systems. 7ntegrated circuits make themainframe computer extremely powerful.

"uch smaller and less expensive than the conventional machines, the minicomputer was first appliedto industrial process control and small%!ob data processing. y the early *+-=s the minis were takingon !obs considered difficult for their larger cousins of a decade earlier. The big machines, in turn, wereperforming tasks previously considered impractical.

The ourth*generation computer is exemplified by the first commercial microprocessor, the 7ntel6--6, introduced in *+*. The central processor unit was put on a single chip. #ith a C


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0LOSSARY OF COMPUTER TERMS

A!!ress% a number used to identify an internal register or a physical location in a memory unit.Algorithm% a set of rules designed to solve a specific problem or carry out a certain procedure.Analog computer % a computer that performs calculations on continuously variable quantities,

represented in the computer by electric voltages or other physical variables.A(D gate% a logic circuit whose output is a logical * if and only if all of its inputs are logical *=s.Assem%l$ language% a language used to operate a digital computer.Au,iliar$ memor$% relatively slow%speed equipment capable of holding large quantities of digitalinformation for example, magnetic disks or tapes.'it % contraction of &binary digit,& a unit of information content. A bit is the smallest unit ofinformation in a binary 'two%valued( system of notation. 7t is the choice between two possible states,usually designated * and -.'$te % eight bits.CD*ROM% compact disk read%only memory. A plastic disk used to permanently store several hundredmillion bytes of data. 1imilar to the compact disks used for audio recording.

Processor Unit% the component of a digital computer consisting of the arithmetic, logical, and controlcircuits.Chip% a small piece of silicon that contains many electric components.Co!e% a system of symbols and rules for their use in representing information.Data% the information to be manipulated by a computer.Data 'an- % a large%scale database, such as that containing all the personnel data for a largecorporation.Data 'ase% the store of information available to a computer in performing a given task.Data Communication % the movement of encoded information over electric transmission systemssuch as telephone lines.Data Processing % the use of a digital computer to store, manipulate, and retrieve nonarithmeticinformation.Digital Computer% a computer that performs arithmetic or logical operations on data in the form ofdiscrete &bits& of information.Enco!e% to convert information represented in one form to another form, for example, to convert itfrom alphabetic and numeric keyboard symbols to patterns of *=s and -=s.lip*lop% an electric circuit in a computer memory capable of holding one bit of information.lopp$ !is- % a form of magnetic disk memory using a floppy plastic disk encased in a protectiveplastic cover and able to store from a few hundred thousand to several million bytes of data.Flo1chart % a diagram used by a programmer to outline the sequence of basic operations to beperformed in a given program.har! !is-% a form of magnetic disk memory using one or stack of rigid disks enclosed in a protectivemetal box and able to store from tens of millions to billions of bytes of data.#ar!1are % the physical equipment that makes up a computer system.#igh*le+el Language % a language used to control the operation of a digital computer withoutreferring to its internal components.&nstruction% a digital%computer word specifying operations to be performed and the addresses of theoperands on which they are to be performed.&ntegrate! Circuit% a very small electric circuit consisting of many interconnected electric devicesand components.


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Logic gate% an electric circuit that performs elementary logical operations.Machine Language % a language used to control the operation of a digital computer which refersspecifically to its internal components.Macro &nstruction% a predefined sequence of assembly%language instructions.Magnetic Dis- Memor$ % a device in which information is stored on spinning disks coated with

magnetic material.Main Memor$% the high%speed memory of a digital computer, containing the program currently beingexecuted and the data being manipulated.Memor$% any device capable of retaining information.Microcomputer% a computer using a microprocessor as its &brain.&Microprocessor% a central processor unit on a chip.Minicomputer% a small low%cost computer designed for small% or medium%si;ed businesses and forscientific use.Mouse% a device used to control the position of a cursor on a display screen and to give commands toa computer.On*line % applies to devices or processes directly controlled by the central processor unit of the

computer.Operan!% a digital%computer word that is the data for some instruction.Operating S$stem% a computer program that provides services to users and maximi;es the use of thecomputer=s resources.Operational Ampliier% an electronic amplifier circuit with additional electric components, used inanalog computers.OR 0ate% a logic circuit whose output is a logical * if one or more of its inputs is a logical *.Pro%lem Language% a high%level language that requires no knowledge on the part of the user otherthat needed to specify the particular problem he or she wants solved.proce!ural language% a high%level language that requires no knowledge on the part of the user otherthan that required to specify the procedure that will solve his or her problem.Program% a sequence of statements that specify the actions to be undertaken by a digital computer. AMachine*Language Program % is a sequence of machine instructions capable of execution by thecomputer, but other programs require a translation step.Ran!om Access% a mode of retrieval of information from the computer=s memory in which particularitems of information may be retrieved without reference to the order in which the information wasoriginally recorded.Real*time% a mode of computer operation in which the computer=s calculations are coordinated with acontinuous flow of data, as in the control of ongoing industrial processes. 7n such operations, thetiming of the computer calculations must take into account &real time&%%the timing of events in theexternal world.Register% a collection of flip%flops treated as a single unit for holding information.Se/uential machine % an interconnected collection of logic gates and memory elements. A digitalcomputer is a sequential machine.Simulation % a procedure in which a computer performs operations to imitate, and thus to predict, thedevelopment of some process, such as the evolution of a star, the depletion of natural resources, oreven the operation of another computer. 7f the nature of the process is uncertain, various possible&models& of it can quickly be tested by determining their consequences through simulation.Sot1are% the programs used by a computer to facilitate its operation and utili;ation.


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File Management.7n the )on Beumann computing architecture, storing data 'including programs( iscrucial. 1ince one of the primary functions of an operating system is to handle important functions forapplication software, file or data management obviously falls to the operating system. Applicationsoftware has no information about where files are actually stored on a disk, or how to retrieve them.

This is stored in the operating system=s access method routines and 'in the case of 9D1%basedmachines( in a file allocation table '@AT(. #hen a program is ready to handle data, it sends a call to theoperating system=s programming interface. This signals the operating system to find and retrieve thefile for the application 'by referring to the @AT and using device drivers to send signals through thedisk controller to the disk drive itself(. This process works in reverse when an application is ready tosave a file to disk.

De+ice Management. "ost computer systems are no longer under the strict design of onemanufacturer, as they were before the advent of the personal computer. 1mall computers are oftenpieced together using keyboards, interface cards, monitors, memory chips, and peripheral devices suchas printers from many different manufacturers. 7t is crucial that the operating system have a method to

keep track of what devices are attached to the system, how they work, and how to direct the input andoutput of signals to and from them.

#hile the operating system provides an information clearinghouse for all devices, it can only do so ifthe device manufacturer has provided detailed instructions. "ost often these instructions are containedin speciali;ed device driver programs that users install whenever a new piece of hardware is added tothe computer. #hen the operating system needs to control the flow of data to or from a piece ofhardware, it calls upon the drivers to do the actual communication.

(et1or- Operating S$stems.Betwork operating systems have a &superset& of functions to handletasks beyond the usual responsibilities of an operating system. These are so distinct from regularoperating system functions that some network operating systems require a regular operating system totake care of basic functions, while they deal only with networking functions.

Betwork operating systems must handle communication among different computers connected to thenetwork. The primary relationship in a classic clientserver network is that between the individualcomputers on the network, called nodes or clients, and the central network controlling computers,called servers. The sharing of devices 'including data storage devices and the information on them( isanother network operating system function. And the access rights to all the devices and information onthe network%%especially when it comes to the enforcement of security%%is the paramount responsibilityof the operating system.

User &nterace.The relationship between an operating system and its user interface '07( is bestsummed up by what technologists call the 078 a shell. The living and vibrant part of an operatingsystem is what is beneath the surface$ the rest of it is !ust exterior work. ut despite what technologiststhink, the user interface is what the world sees of an operating system and it is the point of interactionbetween the user and the operating system.

#istor$.The first design for a computer operating system came from ritish mathematician Charlesabbage '*+5%*/*( as part of his concept for a digital &analytical engine.& The device, designed in


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*/2, was never actually created, and abbage=s work was forgotten until its rediscovery in *+2. 7t isa concept, however, formed the basis for computers and operating systems developed more than acentury later. "ore pioneering work in the design of computer systems by :ungarian mathematicianohn von Beumann '*+-2%*+( led to the development of E9)AC 'electronic discrete variablecomputer(, completed in *+5. 7n the stored%memory or )on Beumann architecture, the operating

system and other instructions program are loaded from a storage device 'a floppy disk or magnetictape, for example( and stored in main memory 'or >A"(. The stored%program method of operation isused by all modern multipurpose computers from personal microcomputers to mainframes.

Mainrame an! Minicomputer Operating S$stems. 1tarting with large mainframe andminicomputer systems designed in the *+-=s and *+4-=s by 7" and 9igital Equipment Corporation,computer operating systems were designed to handle large volumes of instructions. "ainframeoperating systems such as 7"=s ")1 '"ultiple )irtual 1torage(, and minicomputer operating systemssuch as 9EC=s TD


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Apple released its operating system in *+/6 as the "acintosh operating system. 1ince the userinterface is often grafted onto the operating system proper as a &shell,& other companies followed suitby grafting graphical user interfaces, or M07s, onto existing operating systems.

The earliest releases of "icrosoft #indows were shells that used 9D1 as the true operating system.

0nder 0nix, M07s such as "otif, Dpen ?ook, and H #indow concealed the underlying command lineinterface. True graphical operating systems exist on the


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second. 7n ma!or metropolitan areas, the backbone links to routers that provide access to local 71


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k*5 % public schools cc % community colleges tec % technical and vocational schools lib % state, county, and city libraries state % state government agencies

gen % general independent entities cog % councils of government mus % museums dst % districts

Domain names all have 7< address equivalents, which are the only 7nternet addresses 7D"%based encyclopedia that includes text,photographs, and other images. "ultimedia applications can also be very complex, such as a virtualreality arcade game that includes bright, moving graphics and stereo sound.

Multime!ia Computers."ultimedia computers are machines optimi;ed to run applications that use

combined media. "ultimedia applications, especially those that incorporate many video and animationsequences or that frequently draw new graphic images on the screen, require computers capable ofretrieving information from storage and processing and displaying that information without noticeabledelays. A typical multimedia personal computer includes a fast microprocessor to quickly processinstructions. They typically have large amounts 'often *4 megabytes or more for optimum use( ofrandom%access memory '>A"( to hold program instructions and information, and a video acceleratorcard that allows the computer to quickly render graphic images and display them on the monitor. Anaudio card is required to convert digital sound into analog sound waves that can be heard overloudspeakers. @inally, multimedia computers have a C9%>D" drive to play the C9%>D" discs mostmultimedia software programs are stored on.

Apple Computer;s Macintoshcomputer was the leading multimedia computer in the late *+/-=s andearly *++-=s. y *++4, however, virtually all personal computers were configured to run multimediaapplications.

A #istor$ rom #$perte,t."ultimedia came out of work done in the field of hypertext. The ideabehind hypertext was to facilitate nonsequential retrieval of information. #hile traditional text is linearand sequential, hypertext has no order that determines the pattern in which the content is experienced.Each unit of information has a name, such as a node, a script, or a page.


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same as present%day hypertext or multimedia8 it depended on the ability to tie two units of informationtogether.

9oug Engelbart began work on the 1tanford >esearch 7nstitute Augment pro!ect in *+45. B?1 'oB?ine 1ystem( was a part of the Augment pro!ect that allowed researchers to cross%reference the work of

others in their reports and papers by storing all of their work in one shared area. B?1 wasdemonstrated at the *+4/ @all oint Computer Conference. The demonstration used special videopro!ectors and microwave transmission lines between the lab and the conference, and was a forerunnerof interactive computing.

Ted Belson coined the term &hypertext& in *+4. :e developed the Hanadu system, the concept ofwhich was an intermeshing of the entire body of written works. :is large%scale literary vision wasnever created, in part due to storage capacity, not to mention the copyright problems.

The first working hypertext system was the :ypertext Editing 1ystem created in *+4 as a researchpro!ect at rown 0niversity. 7" later sold this system to BA1A=s "anned 1pacecraft Center in

:ouston where it was used to produce documentation for the Apollo missions. 7t was followed up by a*+4/ pro!ect at rown called @>E11 '@ile >etrieval and Editing 1ystem(. oth systems allowed forbasic linking, and were mainly text%based.

:owever, it was not until *+/ that these systems became more like the multimedia known today. 7n*+/, the Aspen "ovie map was developed at what would later become the "7T "edia ?ab. Aspenallowed the user to take a simulated &drive& through the city of Aspen using a computer screen. As inlater computer games, a person would use a !oystick to navigate the virtual space. This system usedtwo screens$ one large screen showed the view of the city, and the other sat below as an overview ormap. The Aspen group later began building instructional repair manuals for cars and bicycles that useda variety of video, image, and text content.

7n *+/2, the Nnowledge "anagement 1ystem, or N"1, was released as a commercial product. Adescendant of the DM research at Carnegie "ellon 0niversity, N"1 ran on 0nix workstations andwas designed to managed large hypertexts with tens of thousands of nodes. That same year, :ypertieswas created at the 0niversity of "aryland. :yperties allowed hyperlinks in text that gave the user ashort definition of where they were going by following a link before actually taking them there.

7n *+/, a program called BoteCards was designed at Herox C 'esearch Center(, andlater became a commercial product. The program created a set of &notecards,& each of which appearedon the computer screen as a new window. That same year, the 1ymbolics workstation came with ahypertext manual called the 1ymbolics 9ocument Examiner, and 7ntermedia was developed at rown0niversity. ?inks in the 7ntermedia system were bi%directional, meaning that a word in one documentlinked to a word in another document, which in turn linked back to the original document.

Muide, the first popular commercial hypertext system, was released for the "acintosh, and later forather than leaving the node to link to another, the links were anchors for text stringsthat would pop up as the user scrolled over or edited the text. y *+/, :yperCard, a BoteCard%likesystem, was produced by Apple Computer. :yperCard quickly became popular in part due to the factthat it was bundled with new "acintosh computers.


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"ultimedia on C9%>D". 7n the mid%*++-=s, hypermedia systems began to gain public recognition dueto the proliferation of C9%>D", or compact disk%read only memory. This optical storage technologyrevolutioni;ed multimedia because of its storage capacity of a floppy disk, and thus a single C9%>D"disc could hold all the text, images, digital audio, and animation needed for a complex multimediaapplication. At first, C9%>D" was most commonly used to store large databases of text documents,

but by *++2, short, black%and%white videos became available on C9%>D", followed quickly byapplications that included full%color video, music, and animation.

Along with the C9%>D" revolution has come data compression standards such as "D" titles were available in themarketplace in *++, and by *++4, thousands of #eb sites included interactive multimedia elements.y the year 5---, it is expected that multimedia will be the norm by which ideas and information arecommunicated among businesses and to consumers.

Definition and History of Computer and Internet

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Transcript of Definition and History of Computer and Internet