【文档说明】计算机科学引论-第二版课件.ppt，共(35)页，802.500 KB，由小橙橙上传

转载请保留链接：https://www.ichengzhen.cn/view-77403.html

以下为本文档部分文字说明：

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

facomputer.Describethethreecomponentsofacomputer:hardware,data,andsoftware.Listtopicsrelatedtocompute

rhardware.Listtopicsrelatedtodata.Listtopicsrelatedtosoftware.Discusssomesocialandethicalissuesrelatedtotheuseofcomputers.

Giveashorthistoryofcomputers.ObjectivesAfterstudyingthischapter,thestudentshouldbeableto:1.31-1TURINGMODELTheid

eaofauniversalcomputationaldevicewasfirstdescribedbyAlanTuringin1937.Heproposedthatallcomputationcouldbeperformedbyaspecialki

ndofamachine,nowcalledaTuringmachine.Hebasedthemodelontheactionsthatpeopleperformwheninvolvedincomputation.He

abstractedtheseactionsintoamodelforacomputationalmachinethathasreallychangedtheworld.1.4DataprocessorsBe

forediscussingtheTuringmodel,letusdefineacomputerasadataprocessor.Usingthisdefinition,acomputeractsasablackboxthatacceptsinputdata,processesthedata,

andcreatesoutputdata(Figure1.1).Althoughthismodelcandefinethefunctionalityofacomputertoday,itistoogeneral.Inthismodel,apocketcalculatorisalsoacompu

ter(whichitis,inaliteralsense).Figure1.1Asinglepurposecomputingmachine1.5ProgrammabledataprocessorsTheTuringm

odelisabettermodelforageneral-purposecomputer.Thismodeladdsanextraelementtothespecificcomputingmachine:theprogr

am.Aprogramisasetofinstructionsthattellsthecomputerwhattodowithdata.Figure1.2showstheTuringmodel.Figure1.2Acompu

terbasedontheTuringmodel1.6Figure1.3Thesameprogram,differentdata1.7Figure1.4Thesamedata,differentprograms1.8Theuniv

ersalTuringmachineAuniversalTuringmachine,amachinethatcandoanycomputationiftheappropriateprogramisprovided,wasthefirstdescriptionofamoderncomputer.I

tcanbeprovedthataverypowerfulcomputerandauniversalTuringmachinecancomputethesamething.Weneedonlyprovidethedataandt

heprogram—thedescriptionofhowtodothecomputation—toeithermachine.Infact,auniversalTuringmachineiscapableofcom

putinganythingthatiscomputable.1.91-2VONNEUMANNMODELComputersbuiltontheTuringuniversalmachinestoredataintheirmemory.Arou

nd1944–1945,JohnvonNeumannproposedthat,sinceprogramanddataarelogicallythesame,programsshouldalsobestoredinthememoryofacomputer.1.10Comp

utersbuiltonthevonNeumannmodeldividethecomputerhardwareintofoursubsystems:memory,arithmeticlogicunit,controlunit,andinput/output(Figure1.5).Fours

ubsystemsFigure1.5ThevonNeumannmodel1.11ThevonNeumannmodelstatesthattheprogrammustbestoredinmemory.Thisistotallydifferentfromthearchitectureo

fearlycomputersinwhichonlythedatawasstoredinmemory:theprogramsfortheirtaskwasimplementedbymanipulatingasetofswitchesorbychangingthewiringsystem.The

memoryofmoderncomputershostsbothaprogramanditscorrespondingdata.Thisimpliesthatboththedataandprogramsshouldhavethesameformat,becausethey

arestoredinmemory.Infact,theyarestoredasbinarypatternsinmemory—asequenceof0sand1s.Thestoredprogramconcept1.12AprograminthevonNeumannmodelisma

deofafinitenumberofinstructions.Inthismodel,thecontrolunitfetchesoneinstructionfrommemory,decodesit,thenexecutesit.Inotherwords,th

einstructionsareexecutedoneafteranother.Ofcourse,oneinstructionmayrequestthecontrolunittojumptosomepreviou

sorfollowinginstruction,butthisdoesnotmeanthattheinstructionsarenotexecutedsequentially.Sequentialexecutionofaprogra

mwastheinitialrequirementofacomputerbasedonthevonNeumannmodel.Today’scomputersexecuteprogramsintheorderthatisthemostefficie

nt.Sequentialexecutionofinstructions1.131-3COMPUTERCOMPONENTSWecanthinkofacomputerasbeingmadeupofthreecomponents:comp

uterhardware,data,andcomputersoftware.1.14ComputerhardwaretodayhasfourcomponentsunderthevonNeumannmodel,althoughwecanhavedifferenttypesofmemory,di

fferenttypesofinput/outputsubsystems,andsoon.WediscusscomputerhardwareinmoredetailinChapter5.ComputerhardwareThevonNeumannmod

elclearlydefinesacomputerasadataprocessingmachinethatacceptstheinputdata,processesit,andoutputstheresul

t.Data1.15ThemainfeatureoftheTuringorvonNeumannmodelsistheconceptoftheprogram.Althoughearlycomputersdidnotstor

etheprograminthecomputer’smemory,theydidusetheconceptofprograms.Programmingthoseearlycomputersmeantchangingthewiringsystemsorturningaseto

fswitchesonoroff.Programmingwasthereforeataskdonebyanoperatororengineerbeforetheactualdataprocessingbegan.Computersoftware1.16Figure1.

6Programanddatainmemory1.17Figure1.7Aprogrammadeofinstructions1.181-4HISTORYInthissectionwebrieflyreviewthehistoryofcomputingan

dcomputers.Wedividethishistoryintothreeperiods.1.19Mechanicalmachines(before1930)Duringthisperiod,severalcomputingmachin

eswereinventedthatbearlittleresemblancetothemodernconceptofacomputer.Inthe17thcentury,BlaisePascal,aFrenchmathemati

cianandphilosopher,inventedPascaline.Inthelate17thcentury,aGermanmathematiciancalledGottfriedLeibnitzinventedwhatisknownasLeibnitz’Wh

eel.ThefirstmachinethatusedtheideaofstorageandprogrammingwastheJacquardloom,inventedbyJoseph-MarieJacquarda

tthebeginningofthe19thcentury.1.20In1823,CharlesBabbageinventedtheDifferenceEngine.Later,heinventedamachinecalledtheAnalytical

Enginethatparallelstheideaofmoderncomputers.In1890,HermanHollerith,workingattheUSCensusBureau,designedan

dbuiltaprogrammermachinethatcouldautomaticallyread,tally,andsortdatastoredonpunchedcards.1.21Thebirthofelectroniccomputers(1930–1950)Between193

0and1950,severalcomputerswereinventedbyscientistswhocouldbeconsideredthepioneersoftheelectroniccompute

rindustry.Theearlycomputersofthisperioddidnotstoretheprograminmemory—allwereprogrammedexternally.Fivecomputerswereprominentduringtheseyears:A

BCZ1MarkI.ColossusENIACEarlyelectroniccomputers1.22ThefirstcomputerbasedonvonNeumann’sideaswasmadein1950attheUniversity

ofPennsylvaniaandwascalledEDVAC.Atthesametime,asimilarcomputercalledEDSACwasbuiltbyMauriceWilkesatCambridgeUniversityinEngland.Computersbasedonthevon

Neumannmodel1.23Computergenerations(1950–present)Computersbuiltafter1950moreorlessfollowthevonNeumannmodel.Theyhavebecomefaster,smaller

,andcheaper,buttheprincipleisalmostthesame.Historiansdividethisperiodintogenerations,witheachgenerationwitnessingsomemajorchangeinhardwareorsoft

ware(butnotinthemodel).Thefirstgeneration(roughly1950–1959)ischaracterizedbytheemergenceofcommercialcomputers.Firstgener

ation1.24Second-generationcomputers(roughly1959–1965)usedtransistorsinsteadofvacuumtubes.Twohigh-levelpr

ogramminglanguages,FORTRANandCOBOLinventedandmadeprogrammingeasier.SecondgenerationTheinventionoftheinteg

ratedcircuitreducedthecostandsizeofcomputersevenfurther.Minicomputersappearedonthemarket.Cannedprograms,popu

larlyknownassoftwarepackages,becameavailable.Thisgenerationlastedroughlyfrom1965to1975.Thirdgeneration1.25Thefourthgenerat

ion(approximately1975–1985)sawtheappearanceofmicrocomputers.Thefirstdesktopcalculator,theAltair8800,becameavailablein1975.Thisgenerat

ionalsosawtheemergenceofcomputernetworks.FourthgenerationThisopen-endedgenerationstartedin1985.Ithaswitnessedthe

appearanceoflaptopandpalmtopcomputers,improvementsinsecondarystoragemedia(CD-ROM,DVDandsoon),theuseofmultimedia,andthephenomenonofvirtual

reality.Fifthgeneration1.261-5SOCIALANDETHICALISSUESComputersciencehascreatedsomeperipheralissues,the

mostprevalentofwhichcanbecategorizedassocialandethicalissues.1.27SocialissuesComputershavecreatedsomearguments.Weintroducesomeofthes

eargumentshere.Somepeoplethinkthatcomputershavecreatedakindofdependency,whichmakespeople’slivesmoredifficult.DependencySocialjusticeisanotheri

ssueweoftenhearabout.Theadvocatesofthisissuearguethatusingcomputersathomeisaluxurybenefitthatnotallpeoplecanaf

ford.Thecostofacomputer,peripheraldevices,andamonthlychargeforInternetaccessisanextraburdenonlow-incomep

eople.Socialjustice1.28Theconceptofdigitaldividecoversboththeissuesofdependencyandsocialjusticediscussedabove.Theconcept

dividessocietyintotwogroups:thosewhoareelectronicallyconnectedtotherestofsocietyandthosewhoarenot.Digitaldivide1.29EthicalissuesComputershav

ecreatedsomeethicalissues.Weintroducesomeofthesehere.Computersallowcommunicationbetweentwopartiestobedoneelectronic

ally.However,muchneedstobedonetomakethistypeofcommunicationprivate.Societyispayingabigpriceforprivateelectroniccommunication.Netwo

rksecuritymaycreatethistypeofprivacy,butitneedseffortandcostsalot.Privacy1.30Anotherethicalissueinacomputerizedsocietyiscopyright:whoownsdata?T

heInternethascreatedopportunitiestoshareideas,buthasalsobroughtwithitafurtherethicalissue:electroniccopyright.CopyrightCompu

tersandinformationtechnologyhavecreatednewtypesofcrime.Hackershavebeenabletoaccessmanycomputersintheworldandhavest

olenalotofmoney.ViruscreatorsdesignnewvirusestobesentthroughtheInternetanddamagetheinformationstoredincomp

uters.Althoughtherearemanyanti-virusprogramsinusetoday,societyispayingabigpriceforthistypeofcrime,whichdidnotexistbeforethecomputerandInterneter

a.Computercrime1.311-6COMPUTERSCIENCEASADISCIPLINEWiththeinventionofcomputers,anewdisciplinehasevolved:co

mputerscience.Likeanyotherdiscipline,computersciencehasnowdividedintoseveralareas.Wecandividetheseareasintotwobroadcategories:systemsareasandappl

icationsareas.Thisbookisabreadth-firstapproachtoalltheseareas.Afterreadingthebook,thereadershouldhaveenoughinformationtosele

ctthedesiredareaofspecialty.1.321-7OUTLINEOFTHECOURSEAfterthisintroductorychapter,thebookisdividedintofiveparts.Par

tI:DatarepresentationandoperationThispartincludesChapters2,3,and4.Chapter2discussesnumbersystems;howaquantitycanberepresent

edusingsymbols.Chapter3discusseshowdifferentdataisstoredinsidethecomputer.Chapter4discussessomeprimitiveoperationsonbits.1.33PartII:Computerha

rdwareThispartincludesChapters5and6.Chapter5givesageneralideaofcomputerhardware,discussingdifferentcomputerorgan

izations.Chapter6showshowindividualcomputersareconnectedtomakecomputernetworksandinternetworks(intern

ets).PartIII:ComputersoftwareThispartincludesChapters7,8,9and10.Chapter7discussesoperatingsystems.Chapter8showshowproblemsolvingisreducedtowritingana

lgorithmfortheproblem.Chapter9takesajourneythroughthelistofcontemporaryprogramminglanguages.Chapter10isareviewofsoftw

areengineering.1.34PartIV:DataorganizationandabstractionPartIVincludesChapters11,12,13and14.Chapter11discus

sdatastructures,collectingdataofthesameordifferenttypeunderonecategory.Chapter12discussesabstractdatatypes.Chapter13showshowdifferentfilestructuresca

nbeusedfordifferentpurposes.Chapter14discussesdatabases.PartV:AdvancedtopicsThispartcoversChapters15

,16,17and18.Chapter15discussesdatacompression.Chapter16exploressomeissuestodowithsecurity.Chapter17discussesthetheoryofcomputation.Chapter18isani

ntroductiontoartificialintelligence,atopicwithday-to-daychallengesincomputerscience.McGraw-Hill©TheMcGraw-

HillCompanies,Inc.,20002021