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1.11IntroductionFoundationsofComputerScienceCengageLearning1.2DefinetheTuringmodelofacomputer.DefinethevonNeumannmodelof

acomputer.Describethethreecomponentsofacomputer:hardware,data,andsoftware.Listtopicsrelatedtocomputerhardware.Listtopicsrelatedtodata

.Listtopicsrelatedtosoftware.Discusssomesocialandethicalissuesrelatedtotheuseofcomputers.Giveashorthistoryofcomputers.

ObjectivesAfterstudyingthischapter,thestudentshouldbeableto:1.31-1TURINGMODELTheideaofauniversalcomputationaldevicewasfirst

describedbyAlanTuringin1937.Heproposedthatallcomputationcouldbeperformedbyaspecialkindofamachine,nowcalledaTuringmachine.Hebasedthemodelontheactions

thatpeopleperformwheninvolvedincomputation.Heabstractedtheseactionsintoamodelforacomputationalmachinethathasreallychangedtheworl

d.1.4DataprocessorsBeforediscussingtheTuringmodel,letusdefineacomputerasadataprocessor.Usingthisdefinition,acomputeractsasablackboxthatacceptsinpu

tdata,processesthedata,andcreatesoutputdata(Figure1.1).Althoughthismodelcandefinethefunctionalityofacomputert

oday,itistoogeneral.Inthismodel,apocketcalculatorisalsoacomputer(whichitis,inaliteralsense).Figure1.1Asinglepurposecomputingmachine1.5Progr

ammabledataprocessorsTheTuringmodelisabettermodelforageneral-purposecomputer.Thismodeladdsanextraelementtothespecificcomputingma

chine:theprogram.Aprogramisasetofinstructionsthattellsthecomputerwhattodowithdata.Figure1.2showstheTuringmodel.Figure1.2AcomputerbasedontheTuringmo

del1.6Figure1.3Thesameprogram,differentdata1.7Figure1.4Thesamedata,differentprograms1.8TheuniversalTuringmach

ineAuniversalTuringmachine,amachinethatcandoanycomputationiftheappropriateprogramisprovided,wasthefirstdescriptionofamoderncomputer.Itcanbepr

ovedthataverypowerfulcomputerandauniversalTuringmachinecancomputethesamething.Weneedonlyprovidethedataandtheprogram—th

edescriptionofhowtodothecomputation—toeithermachine.Infact,auniversalTuringmachineiscapableofcomputinganythingthatiscomputable.1.91-2VONNEUMANN

MODELComputersbuiltontheTuringuniversalmachinestoredataintheirmemory.Around1944–1945,JohnvonNeumannproposedt

hat,sinceprogramanddataarelogicallythesame,programsshouldalsobestoredinthememoryofacomputer.1.10ComputersbuiltonthevonNeumannmodeldivideth

ecomputerhardwareintofoursubsystems:memory,arithmeticlogicunit,controlunit,andinput/output(Figure1.5).FoursubsystemsFigure1.

5ThevonNeumannmodel1.11ThevonNeumannmodelstatesthattheprogrammustbestoredinmemory.Thisistotallydifferentfromthearchitectureofearlycomputersinwh

ichonlythedatawasstoredinmemory:theprogramsfortheirtaskwasimplementedbymanipulatingasetofswitchesorbychangingthe

wiringsystem.Thememoryofmoderncomputershostsbothaprogramanditscorrespondingdata.Thisimpliesthatboththedataandprogramsshouldhavethesameformat

,becausetheyarestoredinmemory.Infact,theyarestoredasbinarypatternsinmemory—asequenceof0sand1s.Thestoredprogramconcept1.12AprograminthevonNeuma

nnmodelismadeofafinitenumberofinstructions.Inthismodel,thecontrolunitfetchesoneinstructionfrommemory,decodesit,thenexecute

sit.Inotherwords,theinstructionsareexecutedoneafteranother.Ofcourse,oneinstructionmayrequestthecontrolunittojumptosomepreviousorfollowinginstruct

ion,butthisdoesnotmeanthattheinstructionsarenotexecutedsequentially.SequentialexecutionofaprogramwastheinitialrequirementofacomputerbasedonthevonN

eumannmodel.Today’scomputersexecuteprogramsintheorderthatisthemostefficient.Sequentialexecutionofinstructions1.131-3COMPUTERCO

MPONENTSWecanthinkofacomputerasbeingmadeupofthreecomponents:computerhardware,data,andcomputersoftware.1.14Computer

hardwaretodayhasfourcomponentsunderthevonNeumannmodel,althoughwecanhavedifferenttypesofmemory,differenttypesofinput/outputsubsystem

s,andsoon.WediscusscomputerhardwareinmoredetailinChapter5.ComputerhardwareThevonNeumannmodelclearlydefinesacomputerasadataproc

essingmachinethatacceptstheinputdata,processesit,andoutputstheresult.Data1.15ThemainfeatureoftheTuringorvonNeumann

modelsistheconceptoftheprogram.Althoughearlycomputersdidnotstoretheprograminthecomputer’smemory,theydidusetheconceptof

programs.Programmingthoseearlycomputersmeantchangingthewiringsystemsorturningasetofswitchesonoroff.Programm

ingwasthereforeataskdonebyanoperatororengineerbeforetheactualdataprocessingbegan.Computersoftware1.16Figure1.6Progr

amanddatainmemory1.17Figure1.7Aprogrammadeofinstructions1.181-4HISTORYInthissectionwebrieflyreviewthehistoryofcomputingandcomputers.Wedi

videthishistoryintothreeperiods.1.19Mechanicalmachines(before1930)Duringthisperiod,severalcomputingmachineswereinventedtha

tbearlittleresemblancetothemodernconceptofacomputer.Inthe17thcentury,BlaisePascal,aFrenchmathematicianandphilosopher,inventedPascaline.In

thelate17thcentury,aGermanmathematiciancalledGottfriedLeibnitzinventedwhatisknownasLeibnitz’Wheel.Thefirstmachinethatusedtheideaofstor

ageandprogrammingwastheJacquardloom,inventedbyJoseph-MarieJacquardatthebeginningofthe19thcentury.1.20In1823,C

harlesBabbageinventedtheDifferenceEngine.Later,heinventedamachinecalledtheAnalyticalEnginethatparallelsthe

ideaofmoderncomputers.In1890,HermanHollerith,workingattheUSCensusBureau,designedandbuiltaprogrammermachinethatcouldautomaticallyread,tally

,andsortdatastoredonpunchedcards.1.21Thebirthofelectroniccomputers(1930–1950)Between1930and1950,sever

alcomputerswereinventedbyscientistswhocouldbeconsideredthepioneersoftheelectroniccomputerindustry.Theearlycomputersofthisperioddid

notstoretheprograminmemory—allwereprogrammedexternally.Fivecomputerswereprominentduringtheseyears:ABCZ1MarkI.

ColossusENIACEarlyelectroniccomputers1.22ThefirstcomputerbasedonvonNeumann’sideaswasmadein1950attheUniversityofPennsylvaniaandwascalledEDVAC.Atthe

sametime,asimilarcomputercalledEDSACwasbuiltbyMauriceWilkesatCambridgeUniversityinEngland.Computersbase

donthevonNeumannmodel1.23Computergenerations(1950–present)Computersbuiltafter1950moreorlessfollowthevonNeumannmodel.Theyhavebecomefaster,smalle

r,andcheaper,buttheprincipleisalmostthesame.Historiansdividethisperiodintogenerations,witheachgenerationwitn

essingsomemajorchangeinhardwareorsoftware(butnotinthemodel).Thefirstgeneration(roughly1950–1959)ischaracte

rizedbytheemergenceofcommercialcomputers.Firstgeneration1.24Second-generationcomputers(roughly1959–1965)us

edtransistorsinsteadofvacuumtubes.Twohigh-levelprogramminglanguages,FORTRANandCOBOLinventedandmadeprogrammingeasier.SecondgenerationTheinv

entionoftheintegratedcircuitreducedthecostandsizeofcomputersevenfurther.Minicomputersappearedonthemarket.Cannedprograms,pop

ularlyknownassoftwarepackages,becameavailable.Thisgenerationlastedroughlyfrom1965to1975.Thirdgeneration1.25Thefourthgene

ration(approximately1975–1985)sawtheappearanceofmicrocomputers.Thefirstdesktopcalculator,theAltair8800,becameavailabl

ein1975.Thisgenerationalsosawtheemergenceofcomputernetworks.FourthgenerationThisopen-endedgenerationstartedin1985.Ithaswitn

essedtheappearanceoflaptopandpalmtopcomputers,improvementsinsecondarystoragemedia(CD-ROM,DVDandsoon),

theuseofmultimedia,andthephenomenonofvirtualreality.Fifthgeneration1.261-5SOCIALANDETHICALISSUESComputersciencehascreatedsomeperipheralissues,the

mostprevalentofwhichcanbecategorizedassocialandethicalissues.1.27SocialissuesComputershavecreatedsomearguments.Weintroducesomeofth

eseargumentshere.Somepeoplethinkthatcomputershavecreatedakindofdependency,whichmakespeople’slivesmoredifficult.DependencySocialjusticeisan

otherissueweoftenhearabout.Theadvocatesofthisissuearguethatusingcomputersathomeisaluxurybenefitthatnotallpeoplecanafford.Thecostofacomputer,pe

ripheraldevices,andamonthlychargeforInternetaccessisanextraburdenonlow-incomepeople.Socialjustice1.28Thecon

ceptofdigitaldividecoversboththeissuesofdependencyandsocialjusticediscussedabove.Theconceptdividessocietyintotwogroups:thosewhoareelectr

onicallyconnectedtotherestofsocietyandthosewhoarenot.Digitaldivide1.29EthicalissuesComputershavecreatedsomeethicalissues.Wei

ntroducesomeofthesehere.Computersallowcommunicationbetweentwopartiestobedoneelectronically.However,muchneeds

tobedonetomakethistypeofcommunicationprivate.Societyispayingabigpriceforprivateelectroniccommunication.Net

worksecuritymaycreatethistypeofprivacy,butitneedseffortandcostsalot.Privacy1.30Anotherethicalissueinacomputeri

zedsocietyiscopyright:whoownsdata?TheInternethascreatedopportunitiestoshareideas,buthasalsobroughtwithitafurtherethicalissue:ele

ctroniccopyright.CopyrightComputersandinformationtechnologyhavecreatednewtypesofcrime.Hackershavebeenabletoaccessman

ycomputersintheworldandhavestolenalotofmoney.ViruscreatorsdesignnewvirusestobesentthroughtheInternetan

ddamagetheinformationstoredincomputers.Althoughtherearemanyanti-virusprogramsinusetoday,societyispayi

ngabigpriceforthistypeofcrime,whichdidnotexistbeforethecomputerandInternetera.Computercrime1.311-6COMPUTERSCIENCEASADIS

CIPLINEWiththeinventionofcomputers,anewdisciplinehasevolved:computerscience.Likeanyotherdiscipline,computersciencehasnowdi

videdintoseveralareas.Wecandividetheseareasintotwobroadcategories:systemsareasandapplicationsareas.Thisbookisabreadth-firstapproachtoallth

eseareas.Afterreadingthebook,thereadershouldhaveenoughinformationtoselectthedesiredareaofspecialty.1.321-7OUTLINEOFTHECOURSEAftert

hisintroductorychapter,thebookisdividedintofiveparts.PartI:DatarepresentationandoperationThispartincludesChapters2,3,and4.Chapter2discussesnumbersyst

ems;howaquantitycanberepresentedusingsymbols.Chapter3discusseshowdifferentdataisstoredinsidethecomputer.Chapter4discussessomeprimi

tiveoperationsonbits.1.33PartII:ComputerhardwareThispartincludesChapters5and6.Chapter5givesageneralideaofcomputerhardware,discuss

ingdifferentcomputerorganizations.Chapter6showshowindividualcomputersareconnectedtomakecomputernetworksandinternetworks(in

ternets).PartIII:ComputersoftwareThispartincludesChapters7,8,9and10.Chapter7discussesoperatingsystems.Chapter8showshowproblemsolvingi

sreducedtowritinganalgorithmfortheproblem.Chapter9takesajourneythroughthelistofcontemporaryprogramminglanguages.Chapter10i

sareviewofsoftwareengineering.1.34PartIV:DataorganizationandabstractionPartIVincludesChapters11,12,13and14.Chapter11discussdatastr

uctures,collectingdataofthesameordifferenttypeunderonecategory.Chapter12discussesabstractdatatypes.Chapter13s

howshowdifferentfilestructurescanbeusedfordifferentpurposes.Chapter14discussesdatabases.PartV:AdvancedtopicsT

hispartcoversChapters15,16,17and18.Chapter15discussesdatacompression.Chapter16exploressomeissuestodowithsecurity.Chapter17d

iscussesthetheoryofcomputation.Chapter18isanintroductiontoartificialintelligence,atopicwithday-to-daychallengesi

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