外文翻译computerprogram英文.docx

外文翻译computerprogram英文.docx

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外文翻译computerprogram英文

ComputerProgram

1Introduction

ComputerProgram,setofinstructionsthatdirectsacomputertoperformsomeprocessingfunctionorcombinationoffunctions.Fortheinstructionstobecarriedout,acomputermustexecuteaprogram,thatis,thecomputerreadstheprogram,andthenfollowthestepsencodedintheprograminapreciseorderuntilcompletion.Aprogramcanbeexecutedmanydifferenttimes,witheachexecutionyieldingapotentiallydifferentresultdependingupontheoptionsanddatathattheusergivesthecomputer.

Programsfallintotwomajorclasses:

applicationprogramsandoperatingsystems.Anapplicationprogramisonethatcarriesoutsomefunctiondirectlyforauser,suchaswordprocessingorgame-playing.Anoperatingsystemisaprogramthatmanagesthecomputerandthevariousresourcesanddevicesconnectedtoit,suchasRAM,harddrives,monitors,keyboards,printers,andmodems,sothattheymaybeusedbyotherprograms.ExamplesofoperatingsystemsareDOS,Windows95,OS\2,andUNIX.

2ProgramDevelopment

Softwaredesignerscreatenewprogramsbyusingspecialapplicationsprograms,oftencalledutilityprogramsordevelopmentprograms.Aprogrammerusesanothertypeofprogramcalledatexteditortowritethenewprograminaspecialnotationcalledaprogramminglanguage.Withthetexteditor,theprogrammercreatesatextfile,whichisanorderedlistofinstructions,alsocalledtheprogramsourcefile.Theindividualinstructionsthatmakeuptheprogramsourcefilearecalledsourcecode.Atthispoint,aspecialapplicationsprogramtranslatesthesourcecodeintomachinelanguage,orobjectcode—aformatthattheoperatingsystemwillrecognizeasaproperprogramandbeabletoexecute.

Threetypesofapplicationsprogramstranslatefromsourcecodetoobjectcode:

compilers,interpreters,andassemblers.Thethreeoperatedifferentlyandondifferenttypesofprogramminglanguages,buttheyservethesamepurposeoftranslatingfromaprogramminglanguageintomachinelanguage.

Acompilertranslatestextfileswritteninahigh-levelprogramminglanguage--suchasFORTRAN,C,orPascal—fromthesourcecodetotheobjectcodeallatonce.ThisdiffersfromtheapproachtakenbyinterpretedlanguagessuchasBASIC,APLandLISP,inwhichaprogramistranslatedintoobjectcodestatementbystatementaseachinstructionisexecuted.Theadvantagetointerpretedlanguagesisthattheycanbeginexecutingtheprogramimmediatelyinsteadofhavingtowaitforallofthesourcecodetobecompiled.Changescanalsobemadetotheprogramfairlyquicklywithouthavingtowaitforittobecompiledagain.Thedisadvantageofinterpretedlanguagesisthattheyareslowtoexecute,sincetheentireprogrammustbetranslatedoneinstructionatatime,eachtimetheprogramisrun.Ontheotherhand,compiledlanguagesarecompiledonlyonceandthuscanbeexecutedbythecomputermuchmorequicklythaninterpretedlanguages.Forthisreason,compiledlanguagesaremorecommonandarealmostalwaysusedinprofessionalandscientificapplications.

Anothertypeoftranslatoristheassembler,whichisusedforprogramsorpartsofprogramswritteninassemblylanguage.Assemblylanguageisanotherprogramminglanguage,butitismuchmoresimilartomachinelanguagethanothertypesofhigh-levellanguages.Inassemblylanguage,asinglestatementcanusuallybetranslatedintoasingleinstructionofmachinelanguage.Today,assemblylanguageisrarelyusedtowriteanentireprogram,butisinsteadmostoftenusedwhentheprogrammerneedstodirectlycontrolsomeaspectofthecomputer’sfunction.

Programsareoftenwrittenasasetofsmallerpieces,witheachpiecerepresentingsomeaspectoftheoverallapplicationprogram.Aftereachpiecehasbeencompiledseparately,aprogramcalledalinkercombinesallofthetranslatedpiecesintoasingleexecutableprogram.

Programsseldomworkcorrectlythefirsttime,soaprogramcalledadebuggerisoftenusedtohelpfindproblemscalledbugs.Debuggingprogramsusuallydetectaneventintheexecutingprogramandpointtheprogrammerbacktotheoriginoftheeventintheprogramcode.

Recentprogrammingsystems,suchasJava,useacombinationofapproachestocreateandexecuteprograms.AcompilertakesaJavasourceprogramandtranslatesitintoanintermediateform.SuchintermediateprogramsarethentransferredovertheInternetintocomputerswhereaninterpreterprogramthenexecutestheintermediateformasanapplicationprogram.

3ProgramElements

Mostprogramsarebuiltfromjustafewkindsofstepsthatarerepeatedmanytimesindifferentcontextsandindifferentcombinationsthroughouttheprogram.Themostcommonstepperformssomecomputation,andthenproceedstothenextstepintheprogram,intheorderspecifiedbytheprogrammer.

Programsoftenneedtorepeatashortseriesofstepsmanytimes,forinstanceinlookingthroughalistofgamescoresandfindingthehighestscore.Suchrepetitivesequencesofcodearecalledloops.

Oneofthecapabilitiesthatmakescomputersousefulistheirabilitytomakeconditionaldecisionsandperformdifferentinstructionsbasedonthevaluesofdatabeingprocessed.If-then-elsestatementsimplementthisfunctionbytestingsomepieceofdataandthenselectingoneoftwosequencesofinstructionsonthebasisoftheresult.Oneoftheinstructionsinthesealternativesmaybeagotostatementthatdirectsthecomputertoselectitsnextinstructionfromadifferentpartoftheprogram.Forexample,aprogrammightcomparetwonumbersandbranchtoadifferentpartoftheprogramdependingontheresultofthecomparison:

Ifxisgreaterthany

Then

Gotoinstruction#10

Elsecontinue

Programoftenuseaspecificsequenceofstepsmorethanonce.Suchasequenceofstepscanbegroupedtogetherintoasubroutine,whichcanthenbecalled,oraccessed,asneededindifferentpartsofthemainprogram.Eachtimeasubroutineiscalled,thecomputerrememberswhereitwasintheprogramwhenthecallwasmade,sothatitcanreturnthereuponcompletionofthesubroutine,allowingaverygeneralpieceofcodetobewrittenonceandusedinmultipleways.

Mostprogramsuseseveralvarietiesofsubroutines.Themostcommonofthesearefunctions,procedures,libraryroutines,systemroutines,anddevicedrivers.Functionsareshortsubroutinesthatcomputesomevalue,suchascomputationsofangles,whichthecomputercannotcomputewithasinglebasicinstruction.Proceduresperformamorecomplexfunction,suchassortingasetofnames.Libraryroutinesaresubroutinesthatarewrittenforusebymanydifferentprograms.Systemroutinesaresimilartolibraryroutinesbutareactuallyfoundintheoperatingsystem.Theyprovidesomeservicefortheapplicationprograms,suchasprintingalineoftext.Devicedriversaresystemroutinesthatareaddedtoanoperatingsystemtoallowthecomputertocommunicatewithanewdevice,suchasascanner,modem,orprinter.Devicedriversoftenhavefeaturesthatcanbeexecuteddirectlyasapplicationsprograms.Thisallowstheusertodirectlycontrolthedevice,whichisusefulif,forinstance,acolorprinterneedstoberealignedtoattainthebestprintingqualityafterchanginganinkcartridge.

4ProgramFunction

Moderncomputersusuallystoreprogramsonsomeformofmagneticstoragemediathatcanbeaccessedrandomlybythecomputer,suchastheharddrivediskpermanentlylocatedinthecomputer,oraportablefloppydisk.Additionalinformationonsuchdisks,calleddirectories,indicatethenamesofthevariousprogrambeginsonthediskmedia.Whenauserdirectsthecomputertoexecuteaparticularapplicationprogram,theoperatingsystemlooksthroughthesedirectories,locatestheprogram,andreadsacopyintoRAM.TheoperatingsystemthendirectstheCPUtostartexecutingtheinstructionsatthebeginningoftheprogram.InstructionsatthebeginningoftheprogrampreparethecomputertoprocessinformationbylocatingfreememorylocationsinRAMtoholdworkingdata,retrievingcopiesofthestandardoptionsanddefaultstheuserhasindicatedfromadisk,anddrawinginitialdisplaysonthemonitor.

Theapplicationprogramrequestscopyofanyinformationtheuserentersbymakingacalltoasystemroutine.Theoperatingsystemconvertsanydatasoenteredintoastandardinternalform.Theapplicationthenusesthisinformationtodecidewhattodonext---forexample,performsomedesiredprocessingfunctionsuchasreformattingapageoftext,orobtainsomeadditionalinformationfromanotherfileonadisk.Ineithercase,callstoothersystemroutinesareusedtoactuallycarryoutthedisplayoftheresultsortheaccessingofthefilefromthedisk.

Whentheapplicationreachescompletionorispromptedtoquit,itmakesfurthersystemcallstomakesurethatalldatathatneedstobesavedhasbeenwrittenbacktodisk.Itthenmakesafinalsystemcalltotheoperatingsystemindicatingthatitisfinished.TheoperatingsystemthenfreesuptheRAMandanydevicethattheapplicationwasusingandawaitsacommandfromtheusertostartanotherprogram.

5History

Peoplehavebeenstoringsequencesofinstructionsintheformofaprogramforseveralcenturies.Musicboxesofthe18thcenturyandplayerpianosofthelate19thandearly20thcenturiesplayedmusicalprogramsstoredasseriesifmetalpins,orholesinpaper,witheachlinerepresentingwhenanotewastobeplayed,andthepinorholeindicatingwhatnotewastobeplayedatthattime.Moreelaboratecontrolofphysicaldevicesbecamecommonintheearly1800swithFrenchinventorJosephMarieJacquard’sinventionofthepunch-cardcontrolledweaving