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1、计算机专业英语Passage(A)CharacteristicsofClientsandServersThetermclientandserverrefertothetwoapplicationsinvolvedinacommunication.Theapplicationthatactivelyinitiatescontactiscalledaclient,whiletheapplicationthatpassivelywaitsforcontactiscalledaserver-Confusionsomctimesar
2、isesoverthetermserver.Formally,thetermreferstoaprogramthatwaitspassivelyforcommunication,andnottothecomputeronwhichexecutes.However,whenacomputerisdedicatedtorunningoneormoreserverprograms,thecomputeritselfissometimes(incorrectly)calledaserver.Hardwarevenderscontr
3、ibutetotheconfusionbecausetheyclassifycomputersthathavefastCPUs,largememories,andpowerfuloperatingsystemsasservermachines.Weadheretoscientifical1yaccurateterminologyandusethetermservertorefertotherunningprogramandnotthecomputer.Thetermserver-classcomputerreferstoa
4、powerfulcomputerusedtorunserversoftware.Informationcanpassineitherorbothdirectionsbetweenaclientandaserver.Typically,aclientsendsarequesttoaserver,andtheserverrcturnsaresponsetotheclient.Insomecases,aclientsendsascriesofrequestsandtheserverissuesaseriesofresponses
5、(e.g-,adatabaseclientmightallowausertolookupmorethanoneitematatime).Inothercases,theserverprovidescontinuousoutputwithoutanyrequest一-assoonastheclientcontactstheserver,theserverbeginssendingdata(e.g.,alocalweatherservermightsendcontinuousweatherreportWithupdatedte
6、mperatureandbarometriepressure).JLtisimportanttounderstandthatserverscanacceptincominginformationaswellasdeliveroutgoinginformation.Forexample,mostfi1eserversareconfiguredtoexportasetoffilestodients,Thatis,aclientsendsarequestthatcontainsafilename,andtheserverresp
7、onsesbysendingacopyofthefile.However,afi1eservercanalsobeconfiguredtoimportfiles(i.e.,toallowaclienttosendacopyofafile,whichtheserveracceptsandstoresondisk).Althoughminorvariationsexist,mostinstancesofclient-serverintcractionhavethesamegeneralcharactcristics.Ingen
8、eral,clientsoftware:•isanarbitraryapplicationthatbecomesaclienttemporarilywhonremoteaccessisneeded,butalsoperformsothercomputationlocally.•isinvokeddire
