操作系统概念 英文版 第六版 (silberschatz 著) 高等教育出版社 课后答案

INSTRUCTORSMANUALTOACCOMPANYOPERATINGSYSTEMCONCEPTSSEVENTHEDITIONABRAHAMSILBERSCHATZYALEUNIVERSITYPETERBAERGALVINCORPORATETECHNOLOGIESGREGGAGNEWESTMINSTERCOLLEGEPREFACETHISVOLUMEISANINSTRUCTORSMANUALFORTHESEVENTHEDITIONOFOPERATINGSYSTEMCONCEPTS,BYABRAHAMSILBERSCHATZ,PETERBAERGALVIN,ANDGREGGAGNEITCONSISTSOFANSWERSTOTHEEXERCISESINTHEPARENTTEXTALTHOUGHWEHAVETRIEDTOPRODUCEANINSTRUCTORSMANUALTHATWILLAIDALLOFTHEUSERSOFOURBOOKASMUCHASPOSSIBLE,THERECANALWAYSBEIMPROVEMENTSIMPROVEDANSWERS,ADDITIONALQUESTIONS,SAMPLETESTQUESTIONS,PROGRAMMINGPROJECTS,ALTERNATIVEORDERSOFPRESENTATIONOFTHEMATERIAL,ADDITIONALREFERENCES,ANDSOONWEINVITEYOUTOHELPUSINIMPROVINGTHISMANUALIFYOUHAVEBETTERSOLUTIONSTOTHEEXERCISESOROTHERITEMSWHICHWOULDBEOFUSEWITHOPERATINGSYSTEMCONCEPTS,WEINVITEYOUTOSENDTHEMTOUSFORCONSIDERATIONINLATEREDITIONSOFTHISMANUALALLCONTRIBUTIONSWILL,OFCOURSE,BEPROPERLYCREDITEDTOTHEIRCONTRIBUTORINTERNETELECTRONICMAILSHOULDBEADDRESSEDTOOSBOOKCSYALEEDUPHYSICALMAILMAYBESENTTOAVISILBERSCHATZ,DEPARTMENTNOFCOMPUTERSCIENCE,YALEUNIVERSITY51PROSPECTSTREET,NEWHAVEN,CT06520,USAASPBGGGCONTENTSCHAPTERINTRODUCTION1CHAPTEROPERATINGSYSTEMSTRUCTURES9CHAPTERPROCESSES15CHAPTERTHREADS23CHAPTERCPUSCHEDULING27CHAPTERPROCESSSYNCHRONIZATION33CHAPTERDEADLOCKS47CHAPTERMEMORYMANAGEMENT55CHAPTERVIRTUALMEMORY61CHAPTERFILESYSTEMSINTERFACE71CHAPTERFILESYSTEMSIMPLEMENTATION75CHAPTERMASSSTORAGESTRUCTURE91CHAPTERI/OSYSTEMS93CHAPTERPROTECTION99CHAPTERSECURITY105CHAPTERNETWORKSTRUCTURES111CHAPTERDISTRIBUTEDCOMMUNICATION117CHAPTERDISTRIBUTEDFILESYSTEMS121CHAPTERMULTIMEDIASYSTEMS127CHAPTEREMBEDDEDSYSTEMS131CHAPTERTHELINUXSYSTEM137CHAPTERWINDOWSXP145CHAPTERINFLUENTIALOPERATINGSYSTEMS149INTRODUCTION1CHAPTERCHAPTER1INTRODUCESTHEGENERALTOPICOFOPERATINGSYSTEMSANDAHANDFULOFIMPORTANTCONCEPTSMULTIPROGRAMMING,TIMESHARING,DISTRIBUTEDSYSTEM,ANDSOONTHEPURPOSEISTOSHOWWHYOPERATINGSYSTEMSAREWHATTHEYAREBYSHOWINGHOWTHEYDEVELOPEDINOPERATINGSYSTEMS,ASINMUCHOFCOMPUTERSCIENCE,WEARELEDTOTHEPRESENTBYTHEPATHSWETOOKINTHEPAST,ANDWECANBETTERUNDERSTANDBOTHTHEPRESENTANDTHEFUTUREBYUNDERSTANDINGTHEPASTADDITIONALWORKTHATMIGHTBECONSIDEREDISLEARNINGABOUTTHEPARTICULARSYSTEMSTHATTHESTUDENTSWILLHAVEACCESSTOATYOURINSTITUTIONTHISISSTILLJUSTAGENERALOVERVIEW,ASSPECIFICINTERFACESARECONSIDEREDINCHAPTER3EXERCISES11INAMULTIPROGRAMMINGANDTIMESHARINGENVIRONMENT,SEVERALUSERSSHARETHESYSTEMSIMULTANEOUSLYTHISSITUATIONCANRESULTINVARIOUSSECURITYPROBLEMSAWHATARETWOSUCHPROBLEMSBCANWEENSURETHESAMEDEGREEOFSECURITYINATIMESHAREDMACHINEASINADEDICATEDMACHINEEXPLAINYOURANSWERANSWERASTEALINGORCOPYINGONESPROGRAMSORDATAUSINGSYSTEMRESOURCESCPU,MEMORY,DISKSPACE,PERIPHERALSWITHOUTPROPERACCOUNTINGBPROBABLYNOT,SINCEANYPROTECTIONSCHEMEDEVISEDBYHUMANSCANINEVITABLYBEBROKENBYAHUMAN,ANDTHEMORECOMPLEXTHESCHEME,THEMOREDIFFICULTITISTOFEELCONFIDENTOFITSCORRECTIMPLEMENTATIONCHAPTER1INTRODUCTION12THEISSUEOFRESOURCEUTILIZATIONSHOWSUPINDIFFERENTFORMSINDIFFERENTTYPESOFOPERATINGSYSTEMSLISTWHATRESOURCESMUSTBEMANAGEDCAREFULLYINTHEFOLLOWINGSETTINGSAMAINFRAMEORMINICOMPUTERSYSTEMSBWORKSTATIONSCONNECTEDTOSERVERSCHANDHELDCOMPUTERSANSWERAMAINFRAMESMEMORYANDCPURESOURCES,STORAGE,NETWORKBANDWIDTHBWORKSTATIONSMEMORYANDCPURESOUCESCHANDHELDCOMPUTERSPOWERCONSUMPTION,MEMORYRESOURCES13UNDERWHATCIRCUMSTANCESWOULDAUSERBEBETTEROFFUSINGATIMESHARINGSYSTEMRATHERTHANAPCORSINGLEUSERWORKSTATIONANSWERWHENTHEREAREFEWOTHERUSERS,THETASKISLARGE,ANDTHEHARDWAREISFAST,TIMESHARINGMAKESSENSETHEFULLPOWEROFTHESYSTEMCANBEBROUGHTTOBEARONTHEUSERSPROBLEMTHEPROBLEMCANBESOLVEDFASTERTHANONAPERSONALCOMPUTERANOTHERCASEOCCURSWHENLOTSOFOTHERUSERSNEEDRESOURCESATTHESAMETIMEAPERSONALCOMPUTERISBESTWHENTHEJOBISSMALLENOUGHTOBEEXECUTEDREASONABLYONITANDWHENPERFORMANCEISSUFFICIENTTOEXECUTETHEPROGRAMTOTHEUSERSSATISFACTION14WHICHOFTHEFUNCTIONALITIESLISTEDBELOWNEEDTOBESUPPORTEDBYTHEOPERATINGSYSTEMFORTHEFOLLOWINGTWOSETTINGSAHANDHELDDEVICESANDBREALTIMESYSTEMSABATCHPROGRAMMINGBVIRTUALMEMORYCTIMESHARINGANSWERFORREALTIMESYSTEMS,THEOPERATINGSYSTEMNEEDSTOSUPPORTVIRTUALMEMORYANDTIMESHARINGINAFAIRMANNERFORHANDHELDSYSTEMS,THEOPERATINGSYSTEMNEEDSTOPROVIDEVIRTUALMEMORY,BUTDOESNOTNEEDTOPROVIDETIMESHARINGBATCHPROGRAMMINGISNOTNECESSARYINBOTHSETTINGS15DESCRIBETHEDIFFERENCESBETWEENSYMMETRICANDASYMMETRICMULTIPROCESSINGWHATARETHREEADVANTAGESANDONEDISADVANTAGEOFMULTIPROCESSORSYSTEMSANSWERSYMMETRICMULTIPROCESSINGTREATSALLPROCESSORSASEQUALS,ANDI/OCANBEPROCESSEDONANYCPUASYMMETRICMULTIPROCESSINGHASONEMASTERCPUANDTHEREMAINDERCPUSARESLAVESTHEMASTERDISTRIBUTESTASKSAMONGTHESLAVES,ANDI/OISUSUALLYDONEBYTHEMASTERONLYMULTIPROCESSORSCANSAVEMONEYBYNOTDUPLICATINGPOWERSUPPLIES,HOUSINGS,ANDPERIPHERALSTHEYCANEXECUTEPROGRAMSMOREQUICKLYANDCANHAVEINCREASEDRELIABILITYTHEYAREALSOMORECOMPLEXINBOTHHARDWAREANDSOFTWARETHANUNIPROCESSORSYSTEMSEXERCISES316HOWDOCLUSTEREDSYSTEMSDIFFERFROMMULTIPROCESSORSYSTEMSWHATISREQUIREDFORTWOMACHINESBELONGINGTOACLUSTERTOCOOPERATETOPROVIDEAHIGHLYAVAILABLESERVICEANSWERCLUSTEREDSYSTEMSARETYPICALLYCONSTRUCTEDBYCOMBININGMULTIPLECOMPUTERSINTOASINGLESYSTEMTOPERFORMACOMPUTATIONALTASKDISTRIBUTEDACROSSTHECLUSTERMULTIPROCESSORSYSTEMSONTHEOTHERHANDCOULDBEASINGLEPHYSICALENTITYCOMPRISINGOFMULTIPLECPUSACLUSTEREDSYSTEMISLESSTIGHTLYCOUPLEDTHANAMULTIPROCESSORSYSTEMCLUSTEREDSYSTEMSCOMMUNICATEUSINGMESSAGES,WHILEPROCESSORSINAMULTIPROCESSORSYSTEMCOULDCOMMUNICATEUSINGSHAREDMEMORYINORDERFORTWOMACHINESTOPROVIDEAHIGHLYAVAILABLESERVICE,THESTATEONTHETWOMACHINESSHOULDBEREPLICATEDANDSHOULDBECONSISTENTLYUPDATEDWHENONEOFTHEMACHINESFAIL,THEOTHERCOULDTHENTAKEOVERTHEFUNCTIONALITYOFTHEFAILEDMACHINE17DISTINGUISHBETWEENTHECLIENTSERVERANDPEERTOPEERMODELSOFDISTRIBUTEDSYSTEMSANSWERTHECLIENTSERVERMODELFIRMLYDISTINGUISHESTHEROLESOFTHECLIENTANDSERVERUNDERTHISMODEL,THECLIENTREQUESTSSERVICESTHATAREPROVIDEDBYTHESERVERTHEPEERTOPEERMODELDOESNTHAVESUCHSTRICTROLESINFACT,ALLNODESINTHESYSTEMARECONSIDEREDPEERSANDTHUSMAYACTASEITHERCLIENTSORSERVERSORBOTHANODEMAYREQUESTASERVICEFROMANOTHERPEER,ORTHENODEMAYINFACTPROVIDESUCHASERVICETOOTHERPEERSINTHESYSTEMFOREXAMPLE,LETSCONSIDERASYSTEMOFNODESTHATSHARECOOKINGRECIPESUNDERTHECLIENTSERVERMODEL,ALLRECIPESARESTOREDWITHTHESERVERIFACLIENTWISHESTOACCESSARECIPE,ITMUSTREQUESTTHERECIPEFROMTHESPECIFIEDSERVERUSINGTHEPEERTOPEERMODEL,APEERNODECOULDASKOTHERPEERNODESFORTHESPECIFIEDRECIPETHENODEORPERHAPSNODESWITHTHEREQUESTEDRECIPECOULDPROVIDEITTOTHEREQUESTINGNODENOTICEHOWEACHPEERMAYACTASBOTHACLIENTIEITMAYREQUESTRECIPESANDASASERVERITMAYPROVIDERECIPES18CONSIDERACOMPUTINGCLUSTERCONSISTINGOFTWONODESRUNNINGADATABASEDESCRIBETWOWAYSINWHICHTHECLUSTERSOFTWARECANMANAGEACCESSTOTHEDATAONTHEDISKDISCUSSTHEBENEFITSANDDISADVANTAGESOFEACHANSWERCONSIDERTHEFOLLOWINGTWOALTERNATIVESASYMMETRICCLUSTERINGANDPARALLELCLUSTERINGWITHASYMMETRICCLUSTERING,ONEHOSTRUNSTHEDATABASEAPPLICATIONWITHTHEOTHERHOSTSIMPLYMONITORINGITIFTHESERVERFAILS,THEMONITORINGHOSTBECOMESTHEACTIVESERVERTHISISAPPROPRIATEFORPROVIDINGREDUNDANCYHOWEVER,ITDOESNOTUTILIZETHEPOTENTIALPROCESSINGPOWEROFBOTHHOSTSWITHPARALLELCLUSTERING,THEDATABASEAPPLICATIONCANRUNINPARALLELONBOTHHOSTSTHEDIFFICULTYIMPLEMENTINGPARALLELCLUSTERSISPROVIDINGSOMEFORMOFDISTRIBUTEDLOCKINGMECHANISMFORFILESONTHESHAREDDISK19HOWARENETWORKCOMPUTERSDIFFERENTFROMTRADITIONALPERSONALCOMPUTERSDESCRIBESOMEUSAGESCENARIOSINWHICHITISADVANTAGEOUSTOUSENETWORKCOMPUTERSANSWERANETWORKCOMPUTERRELIESONACENTRALIZEDCOMPUTERFORMOSTOFITSSERVICESITCANTHEREFOREHAVEAMINIMALOPERATINGSYSTEMCHAPTER1INTRODUCTIONTOMANAGEITSRESOURCESAPERSONALCOMPUTERONTHEOTHERHANDHASTOBECAPABLEOFPROVIDINGALLOFTHEREQUIREDFUNCTIONALITYINASTANDALONEMANNERWITHOUTRELYINGONACENTRALIZEDMANNERSCENARIOSWHEREADMINISTRATIVECOSTSAREHIGHANDWHERESHARINGLEADSTOMOREEFFICIENTUSEOFRESOURCESAREPRECISELYTHOSESETTINGSWHERENETWORKCOMPUTERSAREPREFERRED110WHATISTHEPURPOSEOFINTERRUPTSWHATARETHEDIFFERENCESBETWEENATRAPANDANINTERRUPTCANTRAPSBEGENERATEDINTENTIONALLYBYAUSERPROGRAMIFSO,FORWHATPURPOSEANSWERANINTERRUPTISAHARDWAREGENERATEDCHANGEOFFLOWWITHINTHESYSTEMANINTERRUPTHANDLERISSUMMONEDTODEALWITHTHECAUSEOFTHEINTERRUPTCONTROLISTHENRETURNEDTOTHEINTERRUPTEDCONTEXTANDINSTRUCTIONATRAPISASOFTWAREGENERATEDINTERRUPTANINTERRUPTCANBEUSEDTOSIGNALTHECOMPLETIONOFANI/OTOOBVIATETHENEEDFORDEVICEPOLLINGATRAPCANBEUSEDTOCALLOPERATINGSYSTEMROUTINESORTOCATCHARITHMETICERRORS111DIRECTMEMORYACCESSISUSEDFORHIGHSPEEDI/ODEVICESINORDERTOAVOIDINCREASINGTHECPUSEXECUTIONLOADAHOWDOESTHECPUINTERFACEWITHTHEDEVICETOCOORDINATETHETRANSFERBHOWDOESTHECPUKNOWWHENTHEMEMORYOPERATIONSARECOMPLETECTHECPUISALLOWEDTOEXECUTEOTHERPROGRAMSWHILETHEDMACONTROLLERISTRANSFERRINGDATADOESTHISPROCESSINTERFEREWITHTHEEXECUTIONOFTHEUSERPROGRAMSIFSO,DESCRIBEWHATFORMSOFINTERFERENCEARECAUSEDANSWERTHECPUCANINITIATEADMAOPERATIONBYWRITINGVALUESINTOSPECIALREGISTERSTHATCANBEINDEPENDENTLYACCESSEDBYTHEDEVICETHEDEVICEINITIATESTHECORRESPONDINGOPERATIONONCEITRECEIVESACOMMANDFROMTHECPUWHENTHEDEVICEISFINISHEDWITHITSOPERATION,ITINTERRUPTSTHECPUTOINDICATETHECOMPLETIONOFTHEOPERATIONBOTHTHEDEVICEANDTHECPUCANBEACCESSINGMEMORYSIMULTANEOUSLYTHEMEMORYCONTROLLERPROVIDESACCESSTOTHEMEMORYBUSINAFAIRMANNERTOTHESETWOENTITIESACPUMIGHTTHEREFOREBEUNABLETOISSUEMEMORYOPERATIONSATPEAKSPEEDSSINCEITHASTOCOMPETEWITHTHEDEVICEINORDERTOOBTAINACCESSTOTHEMEMORYBUS112SOMECOMPUTERSYSTEMSDONOTPROVIDEAPRIVILEGEDMODEOFOPERATIONINHARDWAREISITPOSSIBLETOCONSTRUCTASECUREOPERATINGSYSTEMFORTHESECOMPUTERSYSTEMSGIVEARGUMENTSBOTHTHATITISANDTHATITISNOTPOSSIBLEANSWERANOPERATINGSYSTEMFORAMACHINEOFTHISTYPEWOULDNEEDTOREMAININCONTROLORMONITORMODEATALLTIMESTHISCOULDBEACCOMPLISHEDBYTWOMETHODSASOFTWAREINTERPRETATIONOFALLUSERPROGRAMSLIKESOMEBASIC,JAVA,ANDLISPSYSTEMS,FOREXAMPLETHESOFTWAREINTERPRETERWOULDPROVIDE,INSOFTWARE,WHATTHEHARDWAREDOESNOTPROVIDEEXERCISES5BREQUIREMEANTTHATALLPROGRAMSBEWRITTENINHIGHLEVELLANGUAGESSOTHATALLOBJECTCODEISCOMPILERPRODUCEDTHECOMPILERWOULDGENERATEEITHERINLINEORBYFUNCTIONCALLSTHEPROTECTIONCHECKSTHATTHEHARDWAREISMISSING113GIVETWOREASONSWHYCACHESAREUSEFULWHATPROBLEMSDOTHEYSOLVEWHATPROBLEMSDOTHEYCAUSEIFACACHECANBEMADEASLARGEASTHEDEVICEFORWHICHITISCACHINGFORINSTANCE,ACACHEASLARGEASADISK,WHYNOTMAKEITTHATLARGEANDELIMINATETHEDEVICEANSWERCACHESAREUSEFULWHENTWOORMORECOMPONENTSNEEDTOEXCHANGEDATA,ANDTHECOMPONENTSPERFORMTRANSFERSATDIFFERINGSPEEDSCACHESSOLVETHETRANSFERPROBLEMBYPROVIDINGABUFFEROFINTERMEDIATESPEEDBETWEENTHECOMPONENTSIFTHEFASTDEVICEFINDSTHEDATAITNEEDSINTHECACHE,ITNEEDNOTWAITFORTHESLOWERDEVICETHEDATAINTHECACHEMUSTBEKEPTCONSISTENTWITHTHEDATAINTHECOMPONENTSIFACOMPONENTHASADATAVALUECHANGE,ANDTHEDATUMISALSOINTHECACHE,THECACHEMUSTALSOBEUPDATEDTHISISESPECIALLYAPROBLEMONMULTIPROCESSORSYSTEMSWHEREMORETHANONEPROCESSMAYBEACCESSINGADATUMACOMPONENTMAYBEELIMINATEDBYANEQUALSIZEDCACHE,BUTONLYIFATHECACHEANDTHECOMPONENTHAVEEQUIVALENTSTATESAVINGCAPACITYTHATIS,IFTHECOMPONENTRETAINSITSDATAWHENELECTRICITYISREMOVED,THECACHEMUSTRETAINDATAASWELL,ANDBTHECACHEISAFFORDABLE,BECAUSEFASTERSTORAGETENDSTOBEMOREEXPENSIVE114DISCUSS,WITHEXAMPLES,HOWTHEPROBLEMOFMAINTAININGCOHERENCEOFCACHEDDATAMANIFESTSITSELFINTHEFOLLOWINGPROCESSINGENVIRONMENTSASINGLEPROCESSORSYSTEMSBMULTIPROCESSORSYSTEMSCDISTRIBUTEDSYSTEMSANSWERINSINGLEPROCESSORSYSTEMS,THEMEMORYNEEDSTOBEUPDATEDWHENAPROCESSORISSUESUPDATESTOCACHEDVALUESTHESEUPDATESCANBEPERFORMEDIMMEDIATELYORINALAZYMANNERINAMULTIPROCESSORSYSTEM,DIFFERENTPROCESSORSMIGHTBECACHINGTHESAMEMEMORYLOCATIONINITSLOCALCACHESWHENUPDATESAREMADE,THEOTHERCACHEDLOCATIONSNEEDTOBEINVALIDATEDORUPDATEDINDISTRIBUTEDSYSTEMS,CONSISTENCYOFCACHEDMEMORYVALUESISNOTANISSUEHOWEVER,CONSISTENCYPROBLEMSMIGHTARISEWHENACLIENTCACHESFILEDATA115DESCRIBEAMECHANISMFORENFORCINGMEMORYPROTECTIONINORDERTOPREVENTAPROGRAMFROMMODIFYINGTHEMEMORYASSOCIATEDWITHOTHERPROGRAMSANSWERTHEPROCESSORCOULDKEEPTRACKOFWHATLOCATIONSAREASSOCIATEDWITHEACHPROCESSANDLIMITACCESSTOLOCATIONSTHATAREOUTSIDEOFAPROGRAMSEXTENTINFORMATIONREGARDINGTHEEXTENTOFAPROGRAMSMEMORYCOULDBEMAINTAINEDBYUSINGBASEANDLIMITSREGISTERSANDBYPERFORMINGACHECKFOREVERYMEMORYACCESS116WHATNETWORKCONFIGURATIONWOULDBESTSUITTHEFOLLOWINGENVIRONMENTSCHAPTER1INTRODUCTIONAADORMITORYFLOORBAUNIVERSITYCAMPUSCASTATEDANATIONANSWERAADORMITORYFLOORALANBAUNIVERSITYCAMPUSALAN,POSSIBLEAWANFORVERYLARGECAMPUSESCASTATEAWANDANATIONAWAN117DEFINETHEESSENTIALPROPERTIESOFTHEFOLLOWINGTYPESOFOPERATINGSYSTEMSABATCHBINTERACTIVECTIMESHARINGDREALTIMEENETWORKFPARALLELGDISTRIBUTEDHCLUSTEREDIHANDHELDANSWERABATCHJOBSWITHSIMILARNEEDSAREBATCHEDTOGETHERANDRUNTHROUGHTHECOMPUTERASAGROUPBYANOPERATORORAUTOMATICJOBSEQUENCERPERFORMANCEISINCREASEDBYATTEMPTINGTOKEEPCPUANDI/ODEVICESBUSYATALLTIMESTHROUGHBUFFERING,OFFLINEOPERATION,SPOOLING,ANDMULTIPROGRAMMINGBATCHISGOODFOREXECUTINGLARGEJOBSTHATNEEDLITTLEINTERACTIONITCANBESUBMITTEDANDPICKEDUPLATERBINTERACTIVETHISSYSTEMISCOMPOSEDOFMANYSHORTTRANSACTIONSWHERETHERESULTSOFTHENEXTTRANSACTIONMAYBEUNPREDICTABLERESPONSETIMENEEDSTOBESHORTSECONDSSINCETHEUSERSUBMITSANDWAITSFORTHERESULTCTIMESHARINGTHISSYSTEMSUSESCPUSCHEDULINGANDMULTIPROGRAMMINGTOPROVIDEECONOMICALINTERACTIVEUSEOFASYSTEMTHECPUSWITCHESRAPIDLYFROMONEUSERTOANOTHERINSTEADOFHAVINGAJOBDEFINEDBYSPOOLEDCARDIMAGES,EACHPROGRAMREADSITSNEXTCONTROLCARDFROMTHETERMINAL,ANDOUTPUTISNORMALLYPRINTEDIMMEDIATELYTOTHESCREENEXERCISES7DREALTIMEOFTENUSEDINADEDICATEDAPPLICATION,THISSYSTEMREADSINFORMATIONFROMSENSORSANDMUSTRESPONDWITHINAFIXEDAMOUNTOFTIMETOENSURECORRECTPERFORMANCEENETWORKPROVIDESOPERATINGSYSTEMFEATURESACROSSANETWORKSUCHASFILESHARINGFSMPUSEDINSYSTEMSWHERETHEREAREMULTIPLECPUSEACHRUNNINGTHESAMECOPYOFTHEOPERATINGSYSTEMCOMMUNICATIONTAKESPLACEACROSSTHESYSTEMBUSGDISTRIBUTEDTHISSYSTEMDISTRIBUTESCOMPUTATIONAMONGSEVERALPHYSICALPROCESSORSTHEPROCESSORSDONOTSHAREMEMORYORACLOCKINSTEAD,EACHPROCESSORHASITSOWNLOCALMEMORYTHEYCOMMUNICATEWITHEACHOTHERTHROUGHVARIOUSCOMMUNICATIONLINES,SUCHASAHIGHSPEEDBUSORLOCALAREANETWORKHCLUSTEREDACLUSTEREDSYSTEMCOMBINESMULTIPLECOMPUTERSINTOASINGLESYSTEMTOPERFORMCOMPUTATIONALTASKDISTRIBUTEDACROSSTHECLUSTERIHANDHELDASMALLCOMPUTERSYSTEMTHATPERFORMSSIMPLETASKSSUCHASCALENDARS,EMAIL,ANDWEBBROWSINGHANDHELDSYSTEMSDIFFERFROMTRADITIONALDESKTOPSYSTEMSWITHSMALLERMEMORYANDDISPLAYSCREENSANDSLOWERPROCESSORS118WHATARETHETRADEOFFSINHERENTINHANDHELDCOMPUTERSANSWERHANDHELDCOMPUTERSAREMUCHSMALLERTHANTRADITIONALDESKTOPPCSTHISRESULTSINSMALLERMEMORY,SMALLERSCREENS,ANDSLOWERPROCESSINGCAPABILITIESTHANASTANDARDDESKTOPPCBECAUSEOFTHESELIMITATIONS,MOSTHANDHELDSCURRENTLYCANPERFORMONLYBASICTASKSSUCHASCALENDARS,EMAIL,ANDSIMPLEWORDPROCESSINGHOWEVER,DUETOTHEIRSMALLSIZE,THEYAREQUITEPORTABLEAND,WHENTHEYAREEQUIPPEDWITHWIRELESSACCESS,CANPROVIDEREMOTEACCESSTOELECTRONICMAILANDTHEWORLDWIDEWEBOPERATINGSYSTEMSTRUCTURES2CHAPTERCHAPTER3ISCONCERNEDWITHTHEOPERATINGSYSTEMINTERFACESTHATUSERSORATLEASTPROGRAMMERSACTUALLYSEESYSTEMCALLSTHETREATMENTISSOMEWHATVAGUESINCEMOREDETAILREQUIRESPICKINGASPECIFICSYSTEMTODISCUSSTHISCHAPTERISBESTSUPPLEMENTEDWITHEXACTLYTHISDETAILFORTHESPECIFICSYSTEMTHESTUDENTSHAVEATHANDIDEALLYTHEYSHOULDSTUDYTHESYSTEMCALLSANDWRITESOMEPROGRAMSMAKINGSYSTEMCALLSTHISCHAPTERALSOTIESTOGETHERSEVERALIMPORTANTCONCEPTSINCLUDINGLAYEREDDESIGN,VIRTUALMACHINES,JAVAANDTHEJAVAVIRTUALMACHINE,SYSTEMDESIGNANDIMPLEMENTATION,SYSTEMGENERATION,ANDTHEPOLICY/MECHANISMDIFFERENCEEXERCISES21THESERVICESANDFUNCTIONSPROVIDEDBYANOPERATINGSYSTEMCANBEDIVIDEDINTOTWOMAINCATEGORIESBRIEFLYDESCRIBETHETWOCATEGORIESANDDISCUSSHOWTHEYDIFFERANSWERONECLASSOFSERVICESPROVIDEDBYANOPERATINGSYSTEMISTOENFORCEPROTECTIONBETWEENDIFFERENTPROCESSESRUNNINGCONCURRENTLYINTHESYSTEMPROCESSESAREALLOWEDTOACCESSONLYTHOSEMEMORYLOCATIONSTHATAREASSOCIATEDWITHTHEIRADDRESSSPACESALSO,PROCESSESARENOTALLOWEDTOCORRUPTFILESASSOCIATEDWITHOTHERUSERSAPROCESSISALSONOTALLOWEDTOACCESSDEVICESDIRECTLYWITHOUTOPERATINGSYSTEMINTERVENTIONTHESECONDCLASSOFSERVICESPROVIDEDBYANOPERATINGSYSTEMISTOPROVIDENEWFUNCTIONALITYTHATISNOTSUPPORTEDDIRECTLYBYTHEUNDERLYINGHARDWAREVIRTUALMEMORYANDFILESYSTEMSARETWOSUCHEXAMPLESOFNEWSERVICESPROVIDEDBYANOPERATINGSYSTEM22LISTFIVESERVICESPROVIDEDBYANOPERATINGSYSTEMTHATAREDESIGNEDTOMAKEITMORECONVENIENTFORUSERSTOUSETHECOMPUTERSYSTEMINWHATCASESITWOULDBEIMPOSSIBLEFORUSERLEVELPROGRAMSTOPROVIDETHESESERVICESEXPLAINANSWERCHAPTER2OPERATINGSYSTEMSTRUCTURESPROGRAMEXECUTIONTHEOPERATINGSYSTEMLOADSTHECONTENTSORSECTIONSOFAFILEINTOMEMORYANDBEGINSITSEXECUTIONAUSERLEVELPROGRAMCOULDNOTBETRUSTEDTOPROPERLYALLOCATECPUTIMEI/OOPERATIONSDISKS,TAPES,SERIALLINES,ANDOTHERDEVICESMUSTBECOMMUNICATEDWITHATAVERYLOWLEVELTHEUSERNEEDONLYSPECIFYTHEDEVICEANDTHEOPERATIONTOPERFORMONIT,WHILETHESYSTEMCONVERTSTHATREQUESTINTODEVICEORCONTROLLERSPECIFICCOMMANDSUSERLEVELPROGRAMSCANNOTBETRUSTEDTOONLYACCESSDEVICESTHEYSHOULDHAVEACCESSTOANDTOONLYACCESSTHEMWHENTHEYAREOTHERWISEUNUSEDFILESYSTEMMANIPULATIONTHEREAREMANYDETAILSINFILECREATION,DELETION,ALLOCATION,ANDNAMINGTHATUSERSSHOULDNOTHAVETOPERFORMBLOCKSOFDISKSPACEAREUSEDBYFILESANDMUSTBETRACKEDDELETINGAFILEREQUIRESREMOVINGTHENAMEFILEINFORMATIONANDFREEINGTHEALLOCATEDBLOCKSPROTECTIONSMUSTALSOBECHECKEDTOASSUREPROPERFILEACCESSUSERPROGRAMSCOULDNEITHERENSUREADHERENCETOPROTECTIONMETHODSNORBETRUSTEDTOALLOCATEONLYFREEBLOCKSANDDEALLOCATEBLOCKSONFILEDELETIONCOMMUNICATIONSMESSAGEPASSINGBETWEENSYSTEMSREQUIRESMESSAGESBETURNEDINTOPACKETSOFINFORMATION,SENTTOTHENETWORKCONTROLLER,TRANSMITTEDACROSSACOMMUNICATIONSMEDIUM,ANDREASSEMBLEDBYTHEDESTINATIONSYSTEMPACKETORDERINGANDDATACORRECTIONMUSTTAKEPLACEAGAIN,USERPROGRAMSMIGHTNOTCOORDINATEACCESSTOTHENETWORKDEVICE,ORTHEYMIGHTRECEIVEPACKETSDESTINEDFOROTHERPROCESSESERRORDETECTIONERRORDETECTIONOCCURSATBOTHTHEHARDWAREANDSOFTWARELEVELSATTHEHARDWARELEVEL,ALLDATATRANSFERSMUSTBEINSPECTEDTOENSURETHATDATAHAVENOTBEENCORRUPTEDINTRANSITALLDATAONMEDIAMUSTBECHECKEDTOBESURETHEYHAVENOTCHANGEDSINCETHEYWEREWRITTENTOTHEMEDIAATTHESOFTWARELEVEL,MEDIAMUSTBECHECKEDFORDATACONSISTENCYFORINSTANCE,DOTHENUMBEROFALLOCATEDANDUNALLOCATEDBLOCKSOFSTORAGEMATCHTHETOTALNUMBERONTHEDEVICETHERE,ERRORSAREFREQUENTLYPROCESSINDEPENDENTFORINSTANCE,THECORRUPTIONOFDATAONADISK,SOTHEREMUSTBEAGLOBALPROGRAMTHEOPERATINGSYSTEMTHATHANDLESALLTYPESOFERRORSALSO,BYHAVINGERRORSPROCESSEDBYTHEOPERATINGSYSTEM,PROCESSESNEEDNOTCONTAINCODETOCATCHANDCORRECTALLTHEERRORSPOSSIBLEONASYSTEM23DESCRIBETHREEGENERALMETHODSFORPASSINGPARAMETERSTOTHEOPERATINGSYSTEMANSWERAPASSPARAMETERSINREGISTERSBREGISTERSPASSSTARTINGADDRESSESOFBLOCKSOFPARAMETERSCPARAMETERSCANBEPLACED,ORPUSHED,ONTOTHESTACKBYTHEPROGRAM,ANDPOPPEDOFFTHESTACKBYTHEOPERATINGSYSTEMEXERCISE