计算机英语课件Unit1 Computer and Computer Science

Unit1ComputerandComputerScienceSectionA:ComputerOverviewI.IntroductionAcomputerisanelectronicdevicethatcanreceiveasetofinstructions,orprogram,andthencarryoutthisprogrambyperformingcalculationsonnumericaldataorbymanipulatingotherformsofinformation.Themodernworldofhightechnologycouldnothavecomeaboutexceptforthedevelopmentofthecomputer.Differenttypesandsizesofcomputersfindusesthroughoutsocietyinthestorageandhandlingofdata,fromsecretgovernmentalfilestobankingtransactionstoprivatehouseholdaccounts.Computershaveopenedupanewerainmanufacturingthroughthetechniquesofautomation,andtheyhaveenhancedmoderncommunicationsystems.Theyareessentialtoolsinalmosteveryfieldofresearchandappliedtechnology,fromconstructingmodelsoftheuniversetoproducingtomorrow’sweatherreports,andtheirusehasinitselfopenedupnewareasofconjecture.Databaseservicesandcomputernetworksmakeavailableagreatvarietyofinformationsources.Thesameadvancedtechniquesalsomakepossibleinvasionsofpersonalandbusinessprivacy.Computercrimehasbecomeoneofthemanyrisksthatarepartofthepriceofmoderntechnology.II.HistoryThefirstaddingmachine,aprecursorofthedigitalcomputer,wasdevisedinthe1642bytheFrenchscientist,mathematician,andphilosopherBlaisePascal.Thisdeviceemployedaseriesoften-toothedwheels,eachtoothrepresentingadigitfrom0to9.Thewheelswereconnectedsothatnumberscouldbeaddedtoeachotherbyadvancingthewheelsbyacorrectnumberofteeth.Inthe1670stheGermanphilosopherandmathematicianGottfriedWilhelmLeibnizimprovedonthismachinebydevisingonthatcouldalsomultiply.TheFrenchinventorJoseph-MarieJacquard,indesigninganautomaticloom,usedthin,perforatedwoodenboardstocontroltheweavingofcomplicateddesigns.Duringthe1880stheAmericanstatisticianHermanHollerithconceivedtheideaofusingperforatedcard,similartoJacquard’sboards,forprocessingdata.Employingasystemthatpassedpunchedcards,overelectricalcontacts,hewasabletocompilestatisticalinformationforthe1890UnitedStatescensus.1.TheAnalyticalEngineAlsointhe19thcentury,theBritishmathematicianandinventorCharlesBabbageworkedouttheprinciplesofthemoderndigitalcomputer.Heconceivedanumberofmachines,suchasDifferenceEngine,thatwasdesignedtohandlecomplicatedmathematicalproblems.ManyhistoriansconsiderBabbageandhisassociate,themathematicianAugustaAdaByron,thetruepioneersofthemoderndigitalcomputer.OneofBabbage’sdesigns,theAnalyticalEngine,hadmanyfeaturesofamoderncomputer.Ithadaninputstreamintheformofadeckofpunchedcards,a“store”forsavingdata,a“mill”forarithmeticoperations,andaprinterthatmadeapermanentrecord.Babbagefailedtoputthisideaintopractice,thoughitwaywellhavebeentechnicallypossibleatthatdate.2.EarlyComputersAnaloguecomputerbegantobebuiltinthelate19thcentury.Earlymodelscalculatedbymeansofrotatingshaftsandgears.Numericalapproximationsofequationstoodifficulttosolveinanyotherwaywereevaluatedwithsuchmachine.LordKelvinbuiltamechanicaltidepredictorthatwasaspecializedanaloguecomputer.DuringWorldWar1and2,mechanicalandlater,electricalanaloguecomputingsystemswereusedastorpedocoursepredictorsinsubmarinesandasbombsightcontrollersinaircraft.AnothersystemwasdesignedtopredictspringfloodsintheMississippiRiverbasin.3.ElectronicComputersDuringWorldWar2,ateamofscientistsandmathematicians,workingatBletchleyPark,northofLondon,createdoneofthefirstall-electronicdigitalcomputers:Colossus.ByDecember1943,Colossus,whichincorporated1500vacuumtubes,wasoperational.ItwasusedbytheteamheadedbyAlanTuring,inthelargelysuccessfulattempttocrackGermanradiomessagesencipheredintheEnigmacode.Independentlyofthis,intheUnitedStates,aprototypeelectronicmachinehadbeenbuiltasearlyas1939,byJohnAtanasoffandCliffordBerryatlowaStateCollege.ThisprototypeandlaterresearchwerecompletedquietlyandlaterovershadowedbythedevelopmentoftheElectronicNumericalIntegratorAndComputer(ENIAC)in1945.ENIACwasgrantedapatent,whichwasoverturneddecadeslater,in1973,whenthemachinewasrevealedtohaveincorporatedprinciplesfirstusedintheAtanasoff-BerryComputer.ENIACcontained18000vacuumtubesandhadaspeedofseveralhundredmultiplicationsperminute,butoriginallyitsprogramwaswiredintotheprocessorandhadtobemanuallyaltered.Latermachineswerebuiltwithprogramstorage,basedontheideasoftheHungarian-AmericanmathematicianjohnvonNeumann.Theinstructions,likethedata,werestoredwithina“memory”,freeingthecomputerfromthespeedlimitationsofthepaper-tapereaderduringexecutionandpermittingproblemstobesolvedwithoutrewiringthecomputer.Theuseofthetransistorincomputersinthelate1950smarkedtheadventofsmaller,faster,andmoreversatilelogicalelementsthanwerepossiblewithvacuum-tubemachines.Becausetransistorsusemuchlesspowerandhaveamuchlongerlife,thisdevelopmentalonewasresponsiblefortheimprovedmachinescalledsecond-generationcomputers.Componentsbecamesmaller,asdidinter-componentspacings,andthesystembecamemuchlessexpensivetobuild.4.IntegratedCircuitsLateinthe1960stheintegratedcircuit,orIC,wasintroduced,makingitpossibleformanytransistorstobefabricatedononesiliconsubstrate,withinterconnectingwiresplatedinplace.TheICresultedinafurtherreductioninprice,size,andfailurerate.Themicroprocessorbecameareali