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1.11IntroductionFoundationsofComputerScienceCengageLearning1.2DefinetheTuringmodelofacomputer.DefinethevonNeumannmodelofacomputer.Describ

ethethreecomponentsofacomputer:hardware,data,andsoftware.Listtopicsrelatedtocomputerhardware.Listtopicsrelatedtodata.Listtopicsrelatedtosoftware.

Discusssomesocialandethicalissuesrelatedtotheuseofcomputers.Giveashorthistoryofcomputers.ObjectivesAfterst

udyingthischapter,thestudentshouldbeableto:1.31-1TURINGMODELTheideaofauniversalcomputationaldevicewasfirstdescribedby

AlanTuringin1937.Heproposedthatallcomputationcouldbeperformedbyaspecialkindofamachine,nowcalledaTuringmachine.Heb

asedthemodelontheactionsthatpeopleperformwheninvolvedincomputation.Heabstractedtheseactionsintoamodelforacomputationalmachineth

athasreallychangedtheworld.1.4DataprocessorsBeforediscussingtheTuringmodel,letusdefineacomputerasadataprocessor.Usingthisdefinition,ac

omputeractsasablackboxthatacceptsinputdata,processesthedata,andcreatesoutputdata(Figure1.1).Althoughthismodelcandefinethefunctionalityofacomputer

today,itistoogeneral.Inthismodel,apocketcalculatorisalsoacomputer(whichitis,inaliteralsense).Figure1.1Asinglepurposecomputingmachine1.5Pr

ogrammabledataprocessorsTheTuringmodelisabettermodelforageneral-purposecomputer.Thismodeladdsanextraelementtothes

pecificcomputingmachine:theprogram.Aprogramisasetofinstructionsthattellsthecomputerwhattodowithdata.Figu

re1.2showstheTuringmodel.Figure1.2AcomputerbasedontheTuringmodel1.6Figure1.3Thesameprogram,differentdata1.7Figure

1.4Thesamedata,differentprograms1.8TheuniversalTuringmachineAuniversalTuringmachine,amachinethatcandoany

computationiftheappropriateprogramisprovided,wasthefirstdescriptionofamoderncomputer.Itcanbeprovedthataverypowerfulcomputerandaunivers

alTuringmachinecancomputethesamething.Weneedonlyprovidethedataandtheprogram—thedescriptionofhowtodothecomputation—toeithermachine.Infac

t,auniversalTuringmachineiscapableofcomputinganythingthatiscomputable.1.91-2VONNEUMANNMODELComputersbuiltontheTuringuniversalmachinestor

edataintheirmemory.Around1944–1945,JohnvonNeumannproposedthat,sinceprogramanddataarelogicallythesame,programsshouldalsobestoredinthememor

yofacomputer.1.10ComputersbuiltonthevonNeumannmodeldividethecomputerhardwareintofoursubsystems:memory,arithmeticlogicunit,controlunit,and

input/output(Figure1.5).FoursubsystemsFigure1.5ThevonNeumannmodel1.11ThevonNeumannmodelstatesthattheprogrammustbestoredinmemory.

Thisistotallydifferentfromthearchitectureofearlycomputersinwhichonlythedatawasstoredinmemory:theprogramsfortheirtaskwasimplementedbymanipula

tingasetofswitchesorbychangingthewiringsystem.Thememoryofmoderncomputershostsbothaprogramanditscorrespondingdata.Thisimpliesthatbot

hthedataandprogramsshouldhavethesameformat,becausetheyarestoredinmemory.Infact,theyarestoredasbinarypat

ternsinmemory—asequenceof0sand1s.Thestoredprogramconcept1.12AprograminthevonNeumannmodelismadeofafinitenumberofinstructions.Int

hismodel,thecontrolunitfetchesoneinstructionfrommemory,decodesit,thenexecutesit.Inotherwords,theinstructionsareexecutedoneaf

teranother.Ofcourse,oneinstructionmayrequestthecontrolunittojumptosomepreviousorfollowinginstruction,butthisdoesnotmeanthattheinstructionsare

notexecutedsequentially.SequentialexecutionofaprogramwastheinitialrequirementofacomputerbasedonthevonNeumannmode

l.Today’scomputersexecuteprogramsintheorderthatisthemostefficient.Sequentialexecutionofinstructions1.131-3COMPUTERCOMPONENTSWecanthinkofacomput

erasbeingmadeupofthreecomponents:computerhardware,data,andcomputersoftware.1.14ComputerhardwaretodayhasfourcomponentsunderthevonN

eumannmodel,althoughwecanhavedifferenttypesofmemory,differenttypesofinput/outputsubsystems,andsoon.Wediscussco

mputerhardwareinmoredetailinChapter5.ComputerhardwareThevonNeumannmodelclearlydefinesacomputerasadataprocessing

machinethatacceptstheinputdata,processesit,andoutputstheresult.Data1.15ThemainfeatureoftheTuringorvo

nNeumannmodelsistheconceptoftheprogram.Althoughearlycomputersdidnotstoretheprograminthecomputer’smemory,theydidusetheconceptofprograms.Progr

ammingthoseearlycomputersmeantchangingthewiringsystemsorturningasetofswitchesonoroff.Programmingwasthereforeataskdonebyanoperatororengineerbeforet

heactualdataprocessingbegan.Computersoftware1.16Figure1.6Programanddatainmemory1.17Figure1.7Aprogrammadeofinstructions1.181-4HISTORYInthissectionw

ebrieflyreviewthehistoryofcomputingandcomputers.Wedividethishistoryintothreeperiods.1.19Mechanicalmachines(before1930)Duringthisperiod,

severalcomputingmachineswereinventedthatbearlittleresemblancetothemodernconceptofacomputer.Inthe17thcentury,BlaisePascal,aFrenchmathematicianandp

hilosopher,inventedPascaline.Inthelate17thcentury,aGermanmathematiciancalledGottfriedLeibnitzinventedwhatiskno

wnasLeibnitz’Wheel.ThefirstmachinethatusedtheideaofstorageandprogrammingwastheJacquardloom,inventedbyJoseph-MarieJacquardatthebeg

inningofthe19thcentury.1.20In1823,CharlesBabbageinventedtheDifferenceEngine.Later,heinventedamachinecalledtheAnalyticalEngi

nethatparallelstheideaofmoderncomputers.In1890,HermanHollerith,workingattheUSCensusBureau,designedandbuiltaprogrammermachine

thatcouldautomaticallyread,tally,andsortdatastoredonpunchedcards.1.21Thebirthofelectroniccomputers(1930–1950)Between1930and195

0,severalcomputerswereinventedbyscientistswhocouldbeconsideredthepioneersoftheelectroniccomputerindustry.

Theearlycomputersofthisperioddidnotstoretheprograminmemory—allwereprogrammedexternally.Fivecomputerswereprominentduringtheseyears:

ABCZ1MarkI.ColossusENIACEarlyelectroniccomputers1.22ThefirstcomputerbasedonvonNeumann’sideaswasmadein1950attheUniversityofP

ennsylvaniaandwascalledEDVAC.Atthesametime,asimilarcomputercalledEDSACwasbuiltbyMauriceWilkesatCambridgeUniversi

tyinEngland.ComputersbasedonthevonNeumannmodel1.23Computergenerations(1950–present)Computersbuiltafter1950moreorlessfollowt

hevonNeumannmodel.Theyhavebecomefaster,smaller,andcheaper,buttheprincipleisalmostthesame.Historiansdividethisperiodintogenerations,witheachge

nerationwitnessingsomemajorchangeinhardwareorsoftware(butnotinthemodel).Thefirstgeneration(roughly1950–1959)isch

aracterizedbytheemergenceofcommercialcomputers.Firstgeneration1.24Second-generationcomputers(roughly1959–1965)usedtransistorsinsteado

fvacuumtubes.Twohigh-levelprogramminglanguages,FORTRANandCOBOLinventedandmadeprogrammingeasier.Secondg

enerationTheinventionoftheintegratedcircuitreducedthecostandsizeofcomputersevenfurther.Minicomputersappearedonthemarket.Cannedprograms,popularlykn

ownassoftwarepackages,becameavailable.Thisgenerationlastedroughlyfrom1965to1975.Thirdgeneration1.25Thefourthgen

eration(approximately1975–1985)sawtheappearanceofmicrocomputers.Thefirstdesktopcalculator,theAltair8800,becameavailablein1975

.Thisgenerationalsosawtheemergenceofcomputernetworks.FourthgenerationThisopen-endedgenerationstartedin1985.Ithaswitnesse

dtheappearanceoflaptopandpalmtopcomputers,improvementsinsecondarystoragemedia(CD-ROM,DVDandsoon),theuseofmultim

edia,andthephenomenonofvirtualreality.Fifthgeneration1.261-5SOCIALANDETHICALISSUESComputersciencehascreatedsomeper

ipheralissues,themostprevalentofwhichcanbecategorizedassocialandethicalissues.1.27SocialissuesComputershavecreatedsomearguments.Wein

troducesomeoftheseargumentshere.Somepeoplethinkthatcomputershavecreatedakindofdependency,whichmakespeople’slivesmoredifficult.De

pendencySocialjusticeisanotherissueweoftenhearabout.Theadvocatesofthisissuearguethatusingcomputersathomeisal

uxurybenefitthatnotallpeoplecanafford.Thecostofacomputer,peripheraldevices,andamonthlychargeforInternetaccessisanextraburdenonlow-incomepe

ople.Socialjustice1.28Theconceptofdigitaldividecoversboththeissuesofdependencyandsocialjusticediscussedabove.T

heconceptdividessocietyintotwogroups:thosewhoareelectronicallyconnectedtotherestofsocietyandthosewhoarenot.Digitaldivide1.29Ethica

lissuesComputershavecreatedsomeethicalissues.Weintroducesomeofthesehere.Computersallowcommunicationbetweentwopartiestobedoneelectronically.

However,muchneedstobedonetomakethistypeofcommunicationprivate.Societyispayingabigpriceforprivateelectroniccommunication.Networksecuritymaycreatethis

typeofprivacy,butitneedseffortandcostsalot.Privacy1.30Anotherethicalissueinacomputerizedsocietyiscopyright:whoownsdata?TheInternet

hascreatedopportunitiestoshareideas,buthasalsobroughtwithitafurtherethicalissue:electroniccopyright.CopyrightComputersand

informationtechnologyhavecreatednewtypesofcrime.Hackershavebeenabletoaccessmanycomputersintheworldandhavestolenalotofmoney.Viruscreatorsdesignnew

virusestobesentthroughtheInternetanddamagetheinformationstoredincomputers.Althoughtherearemanyanti-virusprogramsinusetoday,societyispayingabigpr

iceforthistypeofcrime,whichdidnotexistbeforethecomputerandInternetera.Computercrime1.311-6COMPUTERSCIENCEASADISCIPLINEWiththeinventiono

fcomputers,anewdisciplinehasevolved:computerscience.Likeanyotherdiscipline,computersciencehasnowdividedintoseveralareas.Wecandividetheseareasin

totwobroadcategories:systemsareasandapplicationsareas.Thisbookisabreadth-firstapproachtoalltheseareas.Afterreadingthebook,thereader

shouldhaveenoughinformationtoselectthedesiredareaofspecialty.1.321-7OUTLINEOFTHECOURSEAfterthisintroductorychapter,t

hebookisdividedintofiveparts.PartI:DatarepresentationandoperationThispartincludesChapters2,3,and4.Cha

pter2discussesnumbersystems;howaquantitycanberepresentedusingsymbols.Chapter3discusseshowdifferentdataisstoredinsidethecomputer.Chap

ter4discussessomeprimitiveoperationsonbits.1.33PartII:ComputerhardwareThispartincludesChapters5and6.Chapter5g

ivesageneralideaofcomputerhardware,discussingdifferentcomputerorganizations.Chapter6showshowindividualcomputersareconnectedtomakecomputernet

worksandinternetworks(internets).PartIII:ComputersoftwareThispartincludesChapters7,8,9and10.Chapter7discussesoperatingsystems.Chapter

8showshowproblemsolvingisreducedtowritinganalgorithmfortheproblem.Chapter9takesajourneythroughthelistofcontemporaryprogramminglanguages.Chapter10isa

reviewofsoftwareengineering.1.34PartIV:DataorganizationandabstractionPartIVincludesChapters11,12,13and14.Chapt

er11discussdatastructures,collectingdataofthesameordifferenttypeunderonecategory.Chapter12discussesabstractdatatypes.Chapter13showshowdiffe

rentfilestructurescanbeusedfordifferentpurposes.Chapter14discussesdatabases.PartV:AdvancedtopicsThispartcove

rsChapters15,16,17and18.Chapter15discussesdatacompression.Chapter16exploressomeissuestodowithsecurity.Chapter17discussesth

etheoryofcomputation.Chapter18isanintroductiontoartificialintelligence,atopicwithday-to-daychallengesincomputerscien

ce.McGraw-Hill©TheMcGraw-HillCompanies,Inc.,20002021