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1、三、选择填空Page49Unit3programinterfacesystemuserstorageclassifyunauthorizedcontroldocumentefficientlyfunctiondetectinternalsecuritypasswordinputOperatingsystemformicro,mini,andmainframecomputersperforinmanyservices.Theseservicescanbeclassifiedeitheras“external"or"internal
2、”.Theoperatingsystemprovidesexternalservicesthathelpusersstartprograms,managestoreddata,andmaintainsecurity.You,asthecomputeruser,controltheseexternalfunctions.Usingacommand-line,menu-driven,orGUIuserinterface,anoperatingsystemprovidesyouwithawaytoselecttheprogramsyo
3、uwouldliketouse.Theoperatingsystemalsohelpsyoufind,rename,anddeletedocumentsandotherdatastoredondisksortapes.Onmany,butnotallcomputersystems,theoperatingsystemhelpsyoumaintainsecuritybycheckingyouruser/£＞（用户标识）andpassword,aswellasprotectingyourdatafromunauthorizedacc
4、essandrevisions^修改）.Theoperatingsystemprovidesinternalservicesubehindthescenes”toensurethatthecomputersystemfunctionsefficiently.Theseinternalservicesarenotgenerallyunderyourcontrol.butinsteadarecontrolledbytheoperatingsystemitself.Theoperatingsystemcontrolsinputando
5、utput,allocates^Y^）systemresources,managesthestoragespaceforprogramsanddata,anddetectsequipinentfailurewithoutanydirectionfromyou.Page70Unit4converthigh-levelexecuteprocessorinterpretersendunderstandcommandaccomplishcoderesultingruncompilecreateprocessfileAprogrammin
6、glanguageprovidesthetoolsaprogrammerusestocreatesoftwareandproducealengthylistofinstructions,calledsourcecode,whichdefinesthesoftwareenvironmentineverydetail-whatitlookslike,howtheuserenterscommands,andhowitmanipulatesdata.Acomputer'smicroDrocessorrniderstsndsonlymac
7、hinelanguage.Therefore,instructionswrittenina（n）hieh・levellanguagemustbetranslatedintomachinelanguagebeforeacomputercanusethem.Theprocessoftranslatinginstructionsfromahigh-levellanguageintomachinelanguagecanbaaccomplishedbytwospecialtypesofprograms:compilersandinterp
8、reters・Acompilertranslatesalltheinstructionsinaprogramasasinglebatch（一批），andtheresultingmachinelanguageinstructions,calledobjectcod
