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1.11IntroductionFoundationsofComputerScience?CengageLearning1.11IntroductionFoundationsof1.2DefinetheTuringmodelofacomputer.DefinethevonNeumannmodelofacomputer.Describethethreecomponentsofacomputer:hardware,

data,andsoftware.Listtopicsrelatedtocomputerhardware.Listtopicsrelatedtodata.Listtopicsrelatedtosoftware.Discusssomesocialandethicalissuesrelatedtotheuseof

computers.Giveashorthistoryofcomputers.ObjectivesAfterstudyingthischapter,thestudentshouldbeableto:1.2DefinetheTuringmodelof1.31-1TURINGMODELTheideaofauniversalcomputationaldevicewasfirstdescribedbyAlanTuringin1937.Heproposedthatallcomputationcouldbeperformedbyaspecialkindofamachine,nowcalledaTuringmachine.Hebasedthemodelontheactionsthatpeopleperformwheninvolvedincomputation.Heabstractedtheseactionsintoamodelforacomputationalmachinethathasreallychangedtheworld.1.31-1TURINGMODELTheidea1.4DataprocessorsBeforediscussingtheTuringmodel,letusdefineacomputerasadataprocessor.Usingthisdefinition,acomputeractsasablackboxthatacceptsinputdata,processesthedata,andcreatesoutputdata(Figure1.1).Althoughthismodelcandefinethefunctionalityofacomputertoday,itistoogeneral.Inthismodel,apocketcalculatorisalsoacomputer(whichitis,inaliteralsense).Figure1.1Asinglepurposecomputingmachine1.4DataprocessorsBeforediscu1.5ProgrammabledataprocessorsTheTuringmodelisabettermodelforageneral-purposecomputer.Thismodeladdsanextraelementtothespecificcomputingmachine:theprogram.Aprogramisasetofinstructionsthattellsthecomputerwhattodowithdata.Figure1.2showstheTuringmodel.Figure1.2AcomputerbasedontheTuringmodel1.5Programmabledataprocessor1.6Figure1.3Thesameprogram,differentdata1.6Figure1.3Thesameprogra1.7Figure1.4Thesamedata,differentprograms1.7Figure1.4Thesamedata,1.8TheuniversalTuringmachineAuniversalTuringmachine,amachinethatcandoanycomputationiftheappropriateprogramisprovided,wasthefirstdescriptionofamoderncomputer.ItcanbeprovedthataverypowerfulcomputerandauniversalTuringmachinecancomputethesamething.Weneedonlyprovidethedataandtheprogram—thedescriptionofhowtodothecomputation—toeithermachine.Infact,auniversalTuringmachineiscapableofcomputinganythingthatiscomputable.1.8TheuniversalTuringmachin1.91-2VONNEUMANNMODELComputersbuiltontheTuringuniversalmachinestoredataintheirmemory.Around1944–1945,JohnvonNeumannproposedthat,sinceprogramanddataarelogicallythesame,programsshouldalsobestoredinthememoryofacomputer.1.91-2VONNEUMANNMODELComp1.10ComputersbuiltonthevonNeumannmodeldividethecomputerhardwareintofoursubsystems:memory,arithmeticlogicunit,controlunit,andinput/output(Figure1.5).FoursubsystemsFigure1.5ThevonNeumannmodel1.10Computersbuiltonthevon1.11ThevonNeumannmodelstatesthattheprogrammustbestoredinmemory.Thisistotallydifferentfromthearchitectureofearlycomputersinwhichonlythedatawasstoredinmemory:theprogramsfortheirtaskwasimplementedbymanipulatingasetofswitchesorbychangingthewiringsystem. Thememoryofmoderncomputershostsbothaprogramanditscorrespondingdata.Thisimpliesthatboththedataandprogramsshouldhavethesameformat,becausetheyarestoredinmemory.Infact,theyarestoredasbinarypatternsinmemory—asequenceof0sand1s.Thestoredprogramconcept1.11ThevonNeumannmodelstat1.12AprograminthevonNeumannmodelismadeofafinitenumberofinstructions.Inthismodel,thecontrolunitfetchesoneinstructionfrommemory,decodesit,thenexecutesit.Inotherwords,theinstructionsareexecutedoneafteranother.Ofcourse,oneinstructionmayrequestthecontrolunittojumptosomepreviousorfollowinginstruction,butthisdoesnotmeanthattheinstructionsarenotexecutedsequentially.SequentialexecutionofaprogramwastheinitialrequirementofacomputerbasedonthevonNeumannmodel.Today’scomputersexecuteprogramsintheorderthatisthemostefficient.Sequentialexecutionofinstructions1.12AprograminthevonNeuma1.131-3COMPUTERCOMPONENTSWecanthinkofacomputerasbeingmadeupofthreecomponents:computerhardware,data,andcomputersoftware.1.131-3COMPUTERCOMPONENTSW1.14ComputerhardwaretodayhasfourcomponentsunderthevonNeumannmodel,althoughwecanhavedifferenttypesofmemory,differenttypesofinput/outputsubsystems,andsoon.WediscusscomputerhardwareinmoredetailinChapter5.ComputerhardwareThevonNeumannmodelclearlydefinesacomputerasadataprocessingmachinethatacceptstheinputdata,processesit,andoutputstheresult.Data1.14Computerhardwaretodayha1.15ThemainfeatureoftheTuringorvonNeumannmodelsistheconceptoftheprogram.Althoughearlycomputersdidnotstoretheprograminthecomputer’smemory,theydidusetheconceptofprograms.Programmingthoseearlycomputersmeantchangingthewiringsystemsorturningasetofswitchesonoroff.Programmingwasthereforeataskdonebyanoperatororengineerbeforetheactualdataprocessingbegan.Computersoftware1.15ThemainfeatureoftheTu1.16Figure1.6Programanddatainmemory1.16Figure1.6Programandda1.17Figure1.7Aprogrammadeofinstructions1.17Figure1.7Aprogrammade1.181-4HISTORYInthissectionwebrieflyreviewthehistoryofcomputingandcomputers.Wedividethishistoryintothreeperiods.1.181-4HISTORYInthissecti1.19Mechanicalmachines(before1930)Duringthisperiod,severalcomputingmachineswereinventedthatbearlittleresemblancetothemodernconceptofacomputer.Inthe17thcentury,BlaisePascal,aFrenchmathematicianand

philosopher,inventedPascaline.Inthelate17thcentury,aGermanmathematiciancalledGottfriedLeibnitzinventedwhatisknownasLeibnitz’Wheel.

Thefirstmachinethatusedtheideaofstorageandprogramming

wastheJacquardloom,inventedbyJoseph-MarieJacquardatthe

beginningofthe19thcentury.1.19Mechanicalmachines(befor1.20In1823,CharlesBabbageinventedtheDifferenceEngine.Later,

heinventedamachinecalledtheAnalyticalEnginethatparallels

theideaofmoderncomputers.In1890,HermanHollerith,workingattheUSCensusBureau,

designedandbuiltaprogrammermachinethatcouldautomatically

read,tally,andsortdatastoredonpunchedcards.1.20In1823,CharlesBabbage1.21Thebirthofelectroniccomputers(1930–1950)Between1930and1950,severalcomputerswereinventedbyscientistswhocouldbeconsideredthepioneersoftheelectroniccomputerindustry.Theearlycomputersofthisperioddidnotstoretheprograminmemory—allwereprogrammedexternally.Fivecomputerswereprominentduringtheseyears:ABCZ1MarkI.ColossusENIACEarlyelectroniccomputers1.21Thebirthofelectronicco1.22ThefirstcomputerbasedonvonNeumann’sideaswasmadein1950attheUniversityofPennsylvaniaandwascalledEDVAC.Atthesametime,asimilarcomputercalledEDSACwasbuiltbyMauriceWilkesatCambridgeUniversityinEngland.ComputersbasedonthevonNeumannmodel1.22Thefirstcomputerbasedo1.23Computergenerations(1950–present)Computersbuiltafter1950moreorlessfollowthevonNeumannmodel.Theyhavebecomefaster,smaller,andcheaper,buttheprincipleisalmostthesame.Historiansdividethisperiodintogenerations,witheachgenerationwitnessingsomemajorchangeinhardwareorsoftware(butnotinthemodel).Thefirstgeneration(roughly1950–1959)ischaracterizedbytheemergenceofcommercialcomputers.Firstgeneration1.23Computergenerations(19501.24Second-generationcomputers(roughly1959–1965)usedtransistorsinsteadofvacuumtubes.Twohigh-levelprogramminglanguages,FORTRANandCOBOLinventedandmadeprogrammingeasier.SecondgenerationTheinventionoftheintegratedcircuitreducedthecostandsizeofcomputersevenfurther.Minicomputersappearedonthemarket.Cannedprograms,popularlyknownassoftwarepackages,becameavailable.Thisgenerationlastedroughlyfrom1965to1975.Thirdgeneration1.24Second-generationcomputer1.25Thefourthgeneration(approximately1975–1985)sawtheappearanceofmicrocomputers.Thefirstdesktopcalculator,theAltair8800,becameavailablein1975.Thisgenerationalsosawtheemergenceofcomputernetworks.FourthgenerationThisopen-endedgenerationstartedin1985.Ithaswitnessedtheappearanceoflaptopandpalmtopcomputers,improvementsinsecondarystoragemedia(CD-ROM,DVDandsoon),theuseofmultimedia,andthephenomenonofvirtualreality.Fifthgeneration1.25Thefourthgeneration(app1.261-5SOCIALANDETHICALISSUESComputersciencehascreatedsomeperipheralissues,themostprevalentofwhichcanbecategorizedassocialandethicalissues.1.261-5SOCIALANDETHICALI1.27SocialissuesComputershavecreatedsomearguments.Weintroducesomeoftheseargumentshere.Somepeoplethinkthatcomputershavecreatedakindofdependency,whichmakespeople’slivesmoredifficult.DependencySocialjusticeisanotherissueweoftenhearabout.Theadvocatesofthisissuearguethatusingcomputersathomeisaluxurybenefitthatnotallpeoplecanafford.Thecostofacomputer,peripheraldevices,andamonthlychargeforInternetaccessisanextraburdenonlow-incomepeople.Socialjustice1.27SocialissuesComputershav1.28Theconceptofdigitaldividecoversboththeissuesofdependencyandsocialjusticediscussedabove.Theconceptdividessocietyintotwogroups:thosewhoareelectronicallyconnectedtotherestofsocietyandthosewhoarenot.Digitaldivide1.28Theconceptofdigitaldiv1.29EthicalissuesComputershavecreatedsomeethicalissues.Weintroducesomeofthesehere.Computersallowcommunicationbetweentwopartiestobedoneelectronically.However,muchneedstobedonetomakethistypeofcommunicationprivate.Societyispayingabigpriceforprivateelectroniccommunication.Networksecuritymaycreatethistypeofprivacy,butitneedseffortandcostsalot.Privacy1.29EthicalissuesComputersha1.30Anotherethicalissueinacomputerizedsocietyiscopyright:whoownsdata?TheInternethascreatedopportunitiestoshareideas,buthasalsobroughtwithitafurtherethicalissue:electroniccopyright.CopyrightComputersandinformationtechnologyhavecreatednewtypesofcrime.Hackershavebeenabletoaccessmanycomputersintheworldandhavestolenalotofmoney.ViruscreatorsdesignnewvirusestobesentthroughtheInternetanddamagetheinformationstoredincomputers.Althoughtherearemanyanti-virusprogramsinusetoday,societyispayingabigpriceforthistypeofcrime,whichdidnotexistbeforethecomputerandInternetera.Computercrime1.30Anotherethicalissueina1.311-6COMPUTERSCIENCEASADISCIPLINEWiththeinventionofcomputers,anewdisciplinehasevolved:computerscience.Likeanyotherdiscipline,computersciencehasnowdividedintoseveralareas.Wecandividetheseareasintotwobroadcategories:systemsareasandapplicationsareas.Thisbookisabreadth-firstapproachtoalltheseareas.Afterreadingthebook,thereadershouldhaveenoughinformationtoselectthedesiredareaofspecialty.1.311-6COMPUTERSCIENCEAS1.321-7OUTLINEOFTHECOURSEAfterthisintroductorychapter,thebookisdividedintofiveparts.PartI:DatarepresentationandoperationThispartincludesChapters2,3,and4.Chapter2discussesnumbersystems;howaquantitycanberepresentedusingsymbols.Chapter3discusseshowdifferentdataisstoredinsidethecomputer.Chapter4discussessomeprimitiveoperationsonbits.1.321-7OUTLINEOFTHECOURS1.33PartII:ComputerhardwareThispartincludesChapters5and6.Chapter5givesageneralideaofcomputerhardware,discussingdifferentcomputerorganizations.Chapter6showshowindividualcomputersareconnectedtomakecomputernetworksandinternetworks(internets).PartIII:ComputersoftwareThispartincludesChapters7,8,9and10.Chapter7discussesoperatingsystems.Chapter8showshowproblemsolvingisreducedtowritinganalgorithmfortheproblem.Chapter9takesajourneythroughthelistofcontemporaryprogramminglanguages.Chapter10isareviewofsoftwareengineering.1.33PartII:Computerhardware1.34PartIV:DataorganizationandabstractionPartIVincludesChapters11,12,13and14.Chapter11discussdatastructures,collectingdataofthesameordifferenttypeunderonecategory.Chapter12discussesabstractdatatypes.Chapter13showshowdifferentfilestructurescanbeusedfordifferentpurposes.Chapter14discussesdatabases.PartV:AdvancedtopicsThispartcoversChapters15,16,17and18.Chapter15discussesdatacompression.Chapter16exploressomeissuestodowithsecurity.Chapter17discussesthetheoryofcomputation.Chapter18isanintroductiontoartificialintelligence,atopicwithday-to-daychallengesincomputerscience.1.34PartIV:Dataorganization202120211.361IntroductionFoundationsofComputerScience?CengageLearning1.11IntroductionFoundationsof1.37DefinetheTuringmodelofacomputer.DefinethevonNeumannmodelofacomputer.Describethethreecomponentsofacomputer:hardware,

data,andsoftware.Listtopicsrelatedtocomputerhardware.Listtopicsrelatedtodata.Listtopicsrelatedtosoftware.Discusssomesocialandethicalissuesrelatedtotheuseof

computers.Giveashorthistoryofcomputers.ObjectivesAfterstudyingthischapter,thestudentshouldbeableto:1.2DefinetheTuringmodelof1.381-1TURINGMODELTheideaofauniversalcomputationaldevicewasfirstdescribedbyAlanTuringin1937.Heproposedthatallcomputationcouldbeperformedbyaspecialkindofamachine,nowcalledaTuringmachine.Hebasedthemodelontheactionsthatpeopleperformwheninvolvedincomputation.Heabstractedtheseactionsintoamodelforacomputationalmachinethathasreallychangedtheworld.1.31-1TURINGMODELTheidea1.39DataprocessorsBeforediscussingtheTuringmodel,letusdefineacomputerasadataprocessor.Usingthisdefinition,acomputeractsasablackboxthatacceptsinputdata,processesthedata,andcreatesoutputdata(Figure1.1).Althoughthismodelcandefinethefunctionalityofacomputertoday,itistoogeneral.Inthismodel,apocketcalculatorisalsoacomputer(whichitis,inaliteralsense).Figure1.1Asinglepurposecomputingmachine1.4DataprocessorsBeforediscu1.40ProgrammabledataprocessorsTheTuringmodelisabettermodelforageneral-purposecomputer.Thismodeladdsanextraelementtothespecificcomputingmachine:theprogram.Aprogramisasetofinstructionsthattellsthecomputerwhattodowithdata.Figure1.2showstheTuringmodel.Figure1.2AcomputerbasedontheTuringmodel1.5Programmabledataprocessor1.41Figure1.3Thesameprogram,differentdata1.6Figure1.3Thesameprogra1.42Figure1.4Thesamedata,differentprograms1.7Figure1.4Thesamedata,1.43TheuniversalTuringmachineAuniversalTuringmachine,amachinethatcandoanycomputationiftheappropriateprogramisprovided,wasthefirstdescriptionofamoderncomputer.ItcanbeprovedthataverypowerfulcomputerandauniversalTuringmachinecancomputethesamething.Weneedonlyprovidethedataandtheprogram—thedescriptionofhowtodothecomputation—toeithermachine.Infact,auniversalTuringmachineiscapableofcomputinganythingthatiscomputable.1.8TheuniversalTuringmachin1.441-2VONNEUMANNMODELComputersbuiltontheTuringuniversalmachinestoredataintheirmemory.Around1944–1945,JohnvonNeumannproposedthat,sinceprogramanddataarelogicallythesame,programsshouldalsobestoredinthememoryofacomputer.1.91-2VONNEUMANNMODELComp1.45ComputersbuiltonthevonNeumannmodeldividethecomputerhardwareintofoursubsystems:memory,arithmeticlogicunit,controlunit,andinput/output(Figure1.5).FoursubsystemsFigure1.5ThevonNeumannmodel1.10Computersbuiltonthevon1.46ThevonNeumannmodelstatesthattheprogrammustbestoredinmemory.Thisistotallydifferentfromthearchitectureofearlycomputersinwhichonlythedatawasstoredinmemory:theprogramsfortheirtaskwasimplementedbymanipulatingasetofswitchesorbychangingthewiringsystem. Thememoryofmoderncomputershostsbothaprogramanditscorrespondingdata.Thisimpliesthatboththedataandprogramsshouldhavethesameformat,becausetheyarestoredinmemory.Infact,theyarestoredasbinarypatternsinmemory—asequenceof0sand1s.Thestoredprogramconcept1.11ThevonNeumannmodelstat1.47AprograminthevonNeumannmodelismadeofafinitenumberofinstructions.Inthismodel,thecontrolunitfetchesoneinstructionfrommemory,decodesit,thenexecutesit.Inotherwords,theinstructionsareexecutedoneafteranother.Ofcourse,oneinstructionmayrequestthecontrolunittojumptosomepreviousorfollowinginstruction,butthisdoesnotmeanthattheinstructionsarenotexecutedsequentially.SequentialexecutionofaprogramwastheinitialrequirementofacomputerbasedonthevonNeumannmodel.Today’scomputersexecuteprogramsintheorderthatisthemostefficient.Sequentialexecutionofinstructions1.12AprograminthevonNeuma1.481-3COMPUTERCOMPONENTSWecanthinkofacomputerasbeingmadeupofthreecomponents:computerhardware,data,andcomputersoftware.1.131-3COMPUTERCOMPONENTSW1.49ComputerhardwaretodayhasfourcomponentsunderthevonNeumannmodel,althoughwecanhavedifferenttypesofmemory,differenttypesofinput/outputsubsystems,andsoon.WediscusscomputerhardwareinmoredetailinChapter5.ComputerhardwareThevonNeumannmodelclearlydefinesacomputerasadataprocessingmachinethatacceptstheinputdata,processesit,andoutputstheresult.Data1.14Computerhardwaretodayha1.50ThemainfeatureoftheTuringorvonNeumannmodelsistheconceptoftheprogram.Althoughearlycomputersdidnotstoretheprograminthecomputer’smemory,theydidusetheconceptofprograms.Programmingthoseearlycomputersmeantchangingthewiringsystemsorturningasetofswitchesonoroff.Programmingwasthereforeataskdonebyanoperatororengineerbeforetheactualdataprocessingbegan.Computersoftware1.15ThemainfeatureoftheTu1.51Figure1.6Programanddatainmemory1.16Figure1.6Programandda1.52Figure1.7Aprogrammadeofinstructions1.17Figure1.7Aprogrammade1.531-4HISTORYInthissectionwebrieflyreviewthehistoryofcomputingandcomputers.Wedividethishistoryintothreeperiods.1.181-4HISTORYInthissecti1.54Mechanicalmachines(before1930)Duringthisperiod,severalcomputingmachineswereinventedthatbearlittleresemblancetothemodernconceptofacomputer.Inthe17thcentury,BlaisePascal,aFrenchmathematicianand

philosopher,inventedPascaline.Inthelate17thcentury,aGermanmathematiciancalledGottfriedLeibnitzinventedwhatisknownasLeibnitz’Wheel.

Thefirstmachinethatusedtheideaofstorageandprogramming

wastheJacquardloom,inventedbyJoseph-MarieJacquardatthe

beginningofthe19thcentury.1.19Mechanicalmachines(befor1.55In1823,CharlesBabbageinventedtheDifferenceEngine.Later,

heinventedamachinecalledtheAnalyticalEnginethatparallels

theideaofmoderncomputers.In1890,HermanHollerith,workingattheUSCensusBureau,

designedandbuiltaprogrammermachinethatcouldautomatically

read,tally,andsortdatastoredonpunchedcards.1.20In1823,CharlesBabbage1.56Thebirthofelectroniccomputers(1930–1950)Between1930and1950,severalcomputerswereinventedbyscientistswhocouldbeconsideredthepioneersoftheelectroniccomputerindustry.Theearlycomputersofthisperioddidnotstoretheprograminmemory—allwereprogrammedexternally.Fivecomputerswereprominentduringtheseyears:ABCZ1MarkI.ColossusENIACEarlyelectroniccomputers1.21Thebirthofelectronicco1.57ThefirstcomputerbasedonvonNeumann’sideaswasmadein1950attheUniversityofPennsylvaniaandwascalledEDVAC.Atthesametime,asimilarcomputercalledEDSACwasbuiltbyMauriceWilkesatCambridgeUniversityinEngland.ComputersbasedonthevonNeumannmodel1.22Thefirstcomputerbasedo1.58Computergenerations(1950–present)Computersbuiltafter1950moreorlessfollowthevonNeumannmodel.Theyhavebecomefaster,smaller,andcheaper,buttheprincipleisalmostthesame.Historiansdividethisperiodintogenerations,witheachgenerationwitnessingsomemajorchangeinhardwareorsoftware(butnotinthemodel).Thefirstgeneration(roughly1950–1959)ischaracterizedbytheemergenceofcommercialcomputers.Firstgeneration1.23Computergenerations(19501.59Second-generationcomputers(roughly1959–1965)usedtransistorsinsteadofvacuumtubes.Twohigh-levelprogramminglanguages,FORTRANandCOBOLinventedandmadeprogrammingeasier.SecondgenerationTheinventionoftheintegratedcircuitreducedthecostandsizeofcomputersevenfurther.Minicomputersappearedonthemarket.Cannedprograms,popularlyknownassoftwarepackages,becameavailable.Thisgenerationlastedroughlyfrom1965to1975.Thirdgeneration1.24Second-generationcomputer1.60Thefourthgeneration(approximately1975–1985)sawtheappearanceofmicrocomputers.Thefirstdesktopcalculator,theAltair8800,becameavailablein1975.Thisgenerationalsosawtheemergenceofcomputernetworks.FourthgenerationThisopen-endedgenerationstartedin1985.Ithaswitnessedtheappearanceoflaptopandpalmtopcomputers,improvementsinsecondarystoragemedia(CD-ROM,DVDandsoon),theuseofmultimedia,andthephenomenonofvirtualreality.Fifthgeneration1.25Thefourthgeneration(app1.611-5SOCIALANDETHICALISSUESComputersciencehascreatedsomeperipheralissues,themostprevalentofwhichcanbecategorizedassocialandethicalissues.1.261-5SOCIALANDETHICALI1.62SocialissuesComputershavecreatedsomearguments.Weintroducesomeoftheseargumentshere.Somepeoplethinkthatcomputershavecreatedakindofdependency,whichmakespeople’slivesmoredifficult.DependencySocialjusticeisanotherissueweoftenhearabout.Theadvocatesofthisissuearguethatusingcomputersathomeisaluxurybenefitthatnotallpeoplecanafford.Thecostofacomputer,peripheraldevices,andamonthlychargeforInternetaccessisanextraburdenonlow-incomepeople.Socialjustice1.27SocialissuesComputershav1.63Theconceptofdigitaldividecoversboththeissuesofdependencyandsocialjusticediscussedabove.Theconceptdividessocietyintotwogroups:thosewhoareelectronicallyconnectedtotherestofsocietyandthosewhoarenot.Digitaldivide1.28Theconceptofdigitaldiv1.64EthicalissuesComputershavecreatedsomeethicalissues.Weintroducesomeofthesehere.Computersallowcommunicationbetweentwopartiestobedoneelectronically.However,muchneedstobedonetomakethistypeofcommunicationprivate.Societyispayingabigpriceforprivateelectroniccommunication.Networksecuritymaycreatethistypeofprivacy,butitneedseffortandcostsalot.Privacy1.29EthicalissuesComputersha1.65Anotherethicalissueinacomputerizedsocietyiscopyright:whoownsdata?TheInternethascreatedopportunitiestoshareideas,buthasalsobroughtwithitafurtherethicalissue:electroniccopyright.CopyrightComputersandinformationtec

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