Chapter1:IntroductionChapter1:IntroductionChapter1:IntroductionWhatOperatingSystemsDoComputer-SystemOrganizationComputer-SystemArchitectureOperating-SystemStructureOperating-SystemOperationsProcessManagementMemoryManagementStorageManagementProtectionandSecurityDistributedSystemsSpecial-PurposeSystemsComputingEnvironmentsChapter1:IntroductionWhatOpObjectivesToprovideagrandtourofthemajoroperatingsystemscomponentsToprovidecoverageofbasiccomputersystemorganizationObjectivesToprovideagrandtWhatisanOperatingSystem?Aprogramthatmanagesthecomputerhardware.Aprogramthatactsasanintermediarybetweenauserofacomputerandthecomputerhardware.Operatingsystemgoals:Executeuserprogramsandmakesolvinguserproblemseasier.---basicgoalMakethecomputersystemconvenienttouse.Usethecomputerhardwareinanefficientmanner.WhatisanOperatingSystem?AComputerSystemStructureComputersystemcanbedividedintofourcomponentsHardware–providesbasiccomputingresourcesCPU,memory,I/OdevicesOperatingsystemControlsandcoordinatesuseofhardwareamongvariousapplicationsandusersApplicationprograms–definethewaysinwhichthesystemresourcesareusedtosolvethecomputingproblemsoftheusersWordprocessors,compilers,webbrowsers,databasesystems,videogamesUsersPeople,machines,othercomputersComputerSystemStructureCompuFourComponentsofaComputerSystemFourComponentsofaComputerOperatingSystemDefinitionOSisaresourceallocatorManagesallresourcesDecidesbetweenconflictingrequestsforefficientandfairresourceuseOSisacontrolprogramControlsexecutionofprogramstopreventerrorsandimproperuseofthecomputerOperatingSystemDefinitionOperatingSystemDefinition(Cont.)Nouniversallyaccepteddefinition“Everythingavendorshipswhenyouorderanoperatingsystem”isgoodapproximationButvarieswildly“Theoneprogramrunningatalltimesonthecomputer”isthekernel.Everythingelseiseitherasystemprogram(shipswiththeoperatingsystem)oranapplicationprogramOperatingSystemDefinition(CComputerStartupbootstrapprogramisloadedatpower-uporrebootTypicallystoredinROMorEPROM,generallyknownasfirmwareInitializatesallaspectsofsystemLoadsoperatingsystemkernelandstartsexecutionComputerStartupbootstrapprogComputerSystemOrganizationComputer-systemoperationOneormoreCPUs,devicecontrollersconnectthroughcommonbusprovidingaccesstosharedmemoryConcurrentexecutionofCPUsanddevicescompetingformemorycyclesComputerSystemOrganizationCoComputer-SystemOperationI/OdevicesandtheCPUcanexecuteconcurrently.Eachdevicecontrollerisinchargeofaparticulardevicetype.Eachdevicecontrollerhasalocalbuffer.CPUmovesdatafrom/tomainmemoryto/fromlocalbuffersI/Oisfromthedevicetolocalbufferofcontroller.DevicecontrollerinformsCPUthatithasfinisheditsoperationbycausinganinterrupt.Computer-SystemOperationI/OdCommonFunctionsofInterruptsInterrupttransferscontroltotheinterruptserviceroutinegenerally,throughtheinterruptvector,whichcontainstheaddressesofalltheserviceroutines.Interruptarchitecturemustsavetheaddressoftheinterruptedinstruction.Incominginterruptsaredisabledwhileanotherinterruptisbeingprocessedtopreventalostinterrupt.Atrapisasoftware-generatedinterruptcausedeitherbyanerrororauserrequest.Anoperatingsystemisinterruptdriven.CommonFunctionsofInterruptsInterruptTimelineInterruptTimelineI/OStructureAfterI/Ostarts,controlreturnstouserprogramonlyuponI/Ocompletion.WaitinstructionidlestheCPUuntilthenextinterruptWaitloop(contentionformemoryaccess).AtmostoneI/Orequestisoutstandingatatime,nosimultaneousI/Oprocessing.AfterI/Ostarts,controlreturnstouserprogramwithoutwaitingforI/Ocompletion.Systemcall–requesttotheoperatingsystemtoallowusertowaitforI/Ocompletion.Device-statustablecontainsentryforeachI/Odeviceindicatingitstype,address,andstate.OperatingsystemindexesintoI/Odevicetabletodeterminedevicestatusandtomodifytableentrytoincludeinterrupt.I/OStructureAfterI/Ostarts,TwoI/OMethodsSynchronousAsynchronousTwoI/OMethodsSynchronousAsynDevice-StatusTableDevice-StatusTableStorageStructureMainmemory–onlylargestoragemediathattheCPUcanaccessdirectly.Secondarystorage–extensionofmainmemorythatprovideslargenonvolatilestoragecapacity.Magneticdisks–rigidmetalorglassplatterscoveredwithmagneticrecordingmaterialDisksurfaceislogicallydividedintotracks,whicharesubdividedintosectors.Thediskcontrollerdeterminesthelogicalinteractionbetweenthedeviceandthecomputer.StorageStructureMainmemory–StorageHierarchyStoragesystemsorganizedinhierarchy.SpeedCostVolatilityCaching–copyinginformationintofasterstoragesystem;mainmemorycanbeviewedasalastcacheforsecondarystorage.StorageHierarchyStoragesysteStorage-DeviceHierarchyStorage-DeviceHierarchyPerformanceofVariousLevelsofStorageMovementbetweenlevelsofstoragehierarchycanbeexplicitorimplicitPerformanceofVariousLevelsComputerSystemArchitectureSingleProcessorSystemsACPUManymicroprocessorDevicecontrollersMulticoreProcessorSystemsACPUwithmulti-coreAcoreisaprocessorMultiprocessorSystem(ParallelSystemsorTightlycoupledsystems)Asymmetricmultiprocessing(ASMP)Symmetricmultiprocessing(SMP)ClusteredsystemsManynodesLANComputerSystemArchitectureSiSymmetricmultiprocessingarchitectureSymmetricmultiprocessingarchClusteredsystemsClusteredsystemsSimpleBatchSystemsHireanoperatorUseroperatorAddacardreaderReducesetuptimebybatchingsimilarjobsAutomaticjobsequencing–automaticallytransferscontrolfromonejobtoanother.Firstrudimentaryoperatingsystem.ResidentmonitorinitialcontrolinmonitorcontroltransferstojobwhenjobcompletescontroltransfersbacktomonitorUniprogrammingSimpleBatchSystemsHireanopMemoryLayoutforaSimpleBatchSystemMemoryLayoutforaSimpleBatcardsIBM1401IBM7094IBM1401TapesCardreaderPrintercardsIBM1401IBM7094IBM1401TapeOperatingSystemStructureMultiprogrammingneededforefficiencySingleusercannotkeepCPUandI/OdevicesbusyatalltimesMultiprogrammingorganizesjobs(codeanddata)soCPUalwayshasonetoexecute---toincreaseCPUutilizationAsubsetoftotaljobsinsystemiskeptinmemorysimultaneouslyOnejobselectedandrunviajobschedulingWhenithastowait(forI/Oforexample),OSswitchestoanotherjobTimesharing(multitasking)islogicalextensioninwhichCPUswitchesjobssofrequentlythatuserscaninteractwitheachjobwhileitisrunning,creatinginteractivecomputingResponsetimeshouldbe<1secondEachuserhasatleastoneprogramexecutinginmemoryprocessIfseveraljobsreadytorunatthesametimeCPUschedulingIfprocessesdon’tfitinmemory,swappingmovestheminandouttorunVirtualmemoryallowsexecutionofprocessesnotcompletelyinmemoryOperatingSystemStructureMultMemoryLayoutforMultiprogrammedSystemMemoryLayoutforMultiprogramRunningofUniprogrammingandMultiprogrammingRunningofUniprogrammingandOperating-SystemOperationsInterruptdrivenbyhardwareSoftwareerrororrequestcreatesexceptionortrapDivisionbyzero,requestforoperatingsystemserviceOtherprocessproblemsincludeinfiniteloop,processesmodifyingeachotherortheoperatingsystemDual-modeoperationallowsOStoprotectitselfandothersystemcomponentsUsermodeandkernelmode

ModebitprovidedbyhardwareProvidesabilitytodistinguishwhensystemisrunningusercodeorkernelcodeSomeinstructionsdesignatedasprivileged,onlyexecutableinkernelmodeSystemcallchangesmodetokernel,returnfromcallresetsittouserOperating-SystemOperationsIntTransitionfromUsertoKernelModeTransitionfromUsertoKernelTimerTimertopreventinfiniteloop/processhoggingresourcesSetinterruptafterspecificperiodOperatingsystemdecrementscounterWhencounterzerogenerateaninterruptSetupbeforeschedulingprocesstoregaincontrolorterminateprogramthatexceedsallottedtimeTimerTimertopreventinfiniteProcessManagementAprocessisaprograminexecution.Itisaunitofworkwithinthesystem.Programisapassiveentity,processisanactiveentity.ProcessneedsresourcestoaccomplishitstaskCPU,memory,I/O,filesInitializationdataProcessterminationrequiresreclaimofanyreusableresourcesSingle-threadedprocesshasoneprogramcounterspecifyinglocationofnextinstructiontoexecuteProcessexecutesinstructionssequentially,oneatatime,untilcompletionMulti-threadedprocesshasoneprogramcounterperthreadTypicallysystemhasmanyprocesses,someuser,someoperatingsystemrunningconcurrentlyononeormoreCPUsConcurrencybymultiplexingtheCPUsamongtheprocesses/threadsProcessManagementProcessManagementActivitiesTheoperatingsystemisresponsibleforthefollowingactivitiesinconnectionwithprocessmanagement:CreatinganddeletingbothuserandsystemprocessesSuspendingandresumingprocessesProvidingmechanismsforprocesssynchronizationProvidingmechanismsforprocesscommunicationProvidingmechanismsfordeadlockhandlingProcessManagementActivitiesTMemoryManagementAlldatainmemorybeforeandafterprocessingAllinstructionsinmemoryinordertoexecuteMemorymanagementdetermineswhatisinmemorywhenOptimizingCPUutilizationandcomputerresponsetousersMemorymanagementactivitiesKeepingtrackofwhichpartsofmemoryarecurrentlybeingusedandbywhomDecidingwhichprocesses(orpartsthereof)anddatatomoveintoandoutofmemoryAllocatinganddeallocatingmemoryspaceasneededMemoryManagementAlldatainmStorageManagementOSprovidesuniform,logicalviewofinformationstorageAbstractsphysicalpropertiestologicalstorageunit-fileEachmediumiscontrolledbydevice(i.e.,diskdrive,tapedrive)Varyingpropertiesincludeaccessspeed,capacity,data-transferrate,accessmethod(sequentialorrandom)File-SystemmanagementFilesusuallyorganizedintodirectoriesAccesscontrolonmostsystemstodeterminewhocanaccesswhatOSactivitiesincludeCreatinganddeletingfilesanddirectoriesPrimitivestomanipulatefilesanddirsMappingfilesontosecondarystorageBackupfilesontostable(non-volatile)storagemediaStorageManagementOSprovidesMass-StorageManagementUsuallydisksusedtostoredatathatdoesnotfitinmainmemoryordatathatmustbekeptfora“l(fā)ong”periodoftime.PropermanagementisofcentralimportanceEntirespeedofcomputeroperationhingesondisksubsystemanditsalgorithmsOSactivitiesFree-spacemanagementStorageallocationDiskschedulingSomestorageneednotbefastTertiarystorageincludesopticalstorage,magnetictapeStillmustbemanagedVariesbetweenWORM(write-once,read-many-times)andRW(read-write)Mass-StorageManagementUsuallyI/OSubsystemOnepurposeofOSistohidepeculiaritiesofhardwaredevicesfromtheuserI/OsubsystemresponsibleforMemorymanagementofI/Oincludingbuffering(storingdatatemporarilywhileitisbeingtransferred),caching(storingpartsofdatainfasterstorageforperformance),spooling(theoverlappingofoutputofonejobwithinputofotherjobs)Generaldevice-driverinterfaceDriversforspecifichardwaredevicesI/OSubsystemOnepurposeofOSProtectionandSecurityProtection–anymechanismforcontrollingaccessofprocessesoruserstoresourcesdefinedbytheOSSecurity–defenseofthesystemagainstinternalandexternalattacksHugerange,includingdenial-of-service,worms,viruses,identitytheft,theftofserviceSystemsgenerallyfirstdistinguishamongusers,todeterminewhocandowhatUseridentities(userIDs,securityIDs)includenameandassociatednumber,oneperuserUserIDthenassociatedwithallfiles,processesofthatusertodetermineaccesscontrolGroupidentifier(groupID)allowssetofuserstobedefinedandcontrolsmanaged,thenalsoassociatedwitheachprocess,filePrivilegeescalationallowsusertochangetoeffectiveIDwithmorerightsProtectionandSecurityProtectComputingEnvironmentsTraditionalcomputerBlurringovertimeOfficeenvironmentPCsconnectedtoanetwork,terminalsattachedtomainframeorminicomputersprovidingbatchandtimesharingNowportalsallowingnetworkedandremotesystemsaccesstosameresourcesHomenetworksUsedtobesinglesystem,thenmodemsNowfirewalled,networkedComputingEnvironmentsTraditiComputingEnvironments(Cont.)Client-ServerComputingDumbterminalssupplantedbysmartPCsManysystemsnowservers,respondingtorequestsgeneratedbyclientsCompute-serverprovidesaninterfacetoclienttorequestservices(i.e.database)File-serverprovidesinterfaceforclientstostoreandretrievefilesComputingEnvironments(Cont.)Peer-to-PeerComputingAnothermodelofdistributedsystemP2PdoesnotdistinguishclientsandserversInsteadallnodesareconsideredpeersMayeachactasclient,serverorbothNodemustjoinP2PnetworkRegistersitsservicewithcentrallookupserviceonnetwork,orBroadcastrequestforserviceandrespondtorequestsforserviceviadiscoveryprotocolExamplesincludeNapsterandGnutellaPeer-to-PeerComputingAnotherWeb-BasedComputingWebhasbecomeubiquitousPCsmostprevalentdevicesMoredevicesbecomingnetworkedtoallowwebaccessNewcategoryofdevicestomanagewebtrafficamongsimilarservers:loadbalancersUseofoperatingsystemslikeWindows95,client-side,haveevolvedintoLinuxandWindowsXP,whichcanbeclientsandserversWeb-BasedComputingWebhasbecQ&AQ&AChapter1:IntroductionChapter1:IntroductionChapter1:IntroductionWhatOperatingSystemsDoComputer-SystemOrganizationComputer-SystemArchitectureOperating-SystemStructureOperating-SystemOperationsProcessManagementMemoryManagementStorageManagementProtectionandSecurityDistributedSystemsSpecial-PurposeSystemsComputingEnvironmentsChapter1:IntroductionWhatOpObjectivesToprovideagrandtourofthemajoroperatingsystemscomponentsToprovidecoverageofbasiccomputersystemorganizationObjectivesToprovideagrandtWhatisanOperatingSystem?Aprogramthatmanagesthecomputerhardware.Aprogramthatactsasanintermediarybetweenauserofacomputerandthecomputerhardware.Operatingsystemgoals:Executeuserprogramsandmakesolvinguserproblemseasier.---basicgoalMakethecomputersystemconvenienttouse.Usethecomputerhardwareinanefficientmanner.WhatisanOperatingSystem?AComputerSystemStructureComputersystemcanbedividedintofourcomponentsHardware–providesbasiccomputingresourcesCPU,memory,I/OdevicesOperatingsystemControlsandcoordinatesuseofhardwareamongvariousapplicationsandusersApplicationprograms–definethewaysinwhichthesystemresourcesareusedtosolvethecomputingproblemsoftheusersWordprocessors,compilers,webbrowsers,databasesystems,videogamesUsersPeople,machines,othercomputersComputerSystemStructureCompuFourComponentsofaComputerSystemFourComponentsofaComputerOperatingSystemDefinitionOSisaresourceallocatorManagesallresourcesDecidesbetweenconflictingrequestsforefficientandfairresourceuseOSisacontrolprogramControlsexecutionofprogramstopreventerrorsandimproperuseofthecomputerOperatingSystemDefinitionOperatingSystemDefinition(Cont.)Nouniversallyaccepteddefinition“Everythingavendorshipswhenyouorderanoperatingsystem”isgoodapproximationButvarieswildly“Theoneprogramrunningatalltimesonthecomputer”isthekernel.Everythingelseiseitherasystemprogram(shipswiththeoperatingsystem)oranapplicationprogramOperatingSystemDefinition(CComputerStartupbootstrapprogramisloadedatpower-uporrebootTypicallystoredinROMorEPROM,generallyknownasfirmwareInitializatesallaspectsofsystemLoadsoperatingsystemkernelandstartsexecutionComputerStartupbootstrapprogComputerSystemOrganizationComputer-systemoperationOneormoreCPUs,devicecontrollersconnectthroughcommonbusprovidingaccesstosharedmemoryConcurrentexecutionofCPUsanddevicescompetingformemorycyclesComputerSystemOrganizationCoComputer-SystemOperationI/OdevicesandtheCPUcanexecuteconcurrently.Eachdevicecontrollerisinchargeofaparticulardevicetype.Eachdevicecontrollerhasalocalbuffer.CPUmovesdatafrom/tomainmemoryto/fromlocalbuffersI/Oisfromthedevicetolocalbufferofcontroller.DevicecontrollerinformsCPUthatithasfinisheditsoperationbycausinganinterrupt.Computer-SystemOperationI/OdCommonFunctionsofInterruptsInterrupttransferscontroltotheinterruptserviceroutinegenerally,throughtheinterruptvector,whichcontainstheaddressesofalltheserviceroutines.Interruptarchitecturemustsavetheaddressoftheinterruptedinstruction.Incominginterruptsaredisabledwhileanotherinterruptisbeingprocessedtopreventalostinterrupt.Atrapisasoftware-generatedinterruptcausedeitherbyanerrororauserrequest.Anoperatingsystemisinterruptdriven.CommonFunctionsofInterruptsInterruptTimelineInterruptTimelineI/OStructureAfterI/Ostarts,controlreturnstouserprogramonlyuponI/Ocompletion.WaitinstructionidlestheCPUuntilthenextinterruptWaitloop(contentionformemoryaccess).AtmostoneI/Orequestisoutstandingatatime,nosimultaneousI/Oprocessing.AfterI/Ostarts,controlreturnstouserprogramwithoutwaitingforI/Ocompletion.Systemcall–requesttotheoperatingsystemtoallowusertowaitforI/Ocompletion.Device-statustablecontainsentryforeachI/Odeviceindicatingitstype,address,andstate.OperatingsystemindexesintoI/Odevicetabletodeterminedevicestatusandtomodifytableentrytoincludeinterrupt.I/OStructureAfterI/Ostarts,TwoI/OMethodsSynchronousAsynchronousTwoI/OMethodsSynchronousAsynDevice-StatusTableDevice-StatusTableStorageStructureMainmemory–onlylargestoragemediathattheCPUcanaccessdirectly.Secondarystorage–extensionofmainmemorythatprovideslargenonvolatilestoragecapacity.Magneticdisks–rigidmetalorglassplatterscoveredwithmagneticrecordingmaterialDisksurfaceislogicallydividedintotracks,whicharesubdividedintosectors.Thediskcontrollerdeterminesthelogicalinteractionbetweenthedeviceandthecomputer.StorageStructureMainmemory–StorageHierarchyStoragesystemsorganizedinhierarchy.SpeedCostVolatilityCaching–copyinginformationintofasterstoragesystem;mainmemorycanbeviewedasalastcacheforsecondarystorage.StorageHierarchyStoragesysteStorage-DeviceHierarchyStorage-DeviceHierarchyPerformanceofVariousLevelsofStorageMovementbetweenlevelsofstoragehierarchycanbeexplicitorimplicitPerformanceofVariousLevelsComputerSystemArchitectureSingleProcessorSystemsACPUManymicroprocessorDevicecontrollersMulticoreProcessorSystemsACPUwithmulti-coreAcoreisaprocessorMultiprocessorSystem(ParallelSystemsorTightlycoupledsystems)Asymmetricmultiprocessing(ASMP)Symmetricmultiprocessing(SMP)ClusteredsystemsManynodesLANComputerSystemArchitectureSiSymmetricmultiprocessingarchitectureSymmetricmultiprocessingarchClusteredsystemsClusteredsystemsSimpleBatchSystemsHireanoperatorUseroperatorAddacardreaderReducesetuptimebybatchingsimilarjobsAutomaticjobsequencing–automaticallytransferscontrolfromonejobtoanother.Firstrudimentaryoperatingsystem.ResidentmonitorinitialcontrolinmonitorcontroltransferstojobwhenjobcompletescontroltransfersbacktomonitorUniprogrammingSimpleBatchSystemsHireanopMemoryLayoutforaSimpleBatchSystemMemoryLayoutforaSimpleBatcardsIBM1401IBM7094IBM1401TapesCardreaderPrintercardsIBM1401IBM7094IBM1401TapeOperatingSystemStructureMultiprogrammingneededforefficiencySingleusercannotkeepCPUandI/OdevicesbusyatalltimesMultiprogrammingorganizesjobs(codeanddata)soCPUalwayshasonetoexecute---toincreaseCPUutilizationAsubsetoftotaljobsinsystemiskeptinmemorysimultaneouslyOnejobselectedandrunviajobschedulingWhenithastowait(forI/Oforexample),OSswitchestoanotherjobTimesharing(multitasking)islogicalextensioninwhichCPUswitchesjobssofrequentlythatuserscaninteractwitheachjobwhileitisrunning,creatinginteractivecomputingResponsetimeshouldbe<1secondEachuserhasatleastoneprogramexecutinginmemoryprocessIfseveraljobsreadytorunatthesametimeCPUschedulingIfprocessesdon’tfitinmemory,swappingmovestheminandouttorunVirtualmemoryallowsexecutionofprocessesnotcompletelyinmemoryOperatingSystemStructureMultMemoryLayoutforMultiprogrammedSystemMemoryLayoutforMultiprogramRunningofUniprogrammingandMultiprogrammingRunningofUniprogrammingandOperating-SystemOperationsInterruptdrivenbyhardwareSoftwareerrororrequestcreatesexceptionortrapDivisionbyzero,requestforoperatingsystemserviceOtherprocessproblemsincludeinfiniteloop,processesmodifyingeachotherortheoperatingsystemDual-modeoperationallowsOStoprotectitselfandothersystemcomponentsUsermodeandkernelmode

ModebitprovidedbyhardwareProvidesabilitytodistinguishwhensystemisrunningusercodeorkernelcodeSomeinstructionsdesignatedasprivileged,onlyexecutableinkernelmodeSystemcallchangesmodetokernel,returnfromcallresetsittouserOperating-SystemOperationsIntTransitionfromUsertoKernelModeTransitionfromUsertoKernelTimerTimertopreventinfiniteloop/processhoggingresourcesSetinterruptafterspecificperiodOperatingsystemdecrementscounterWhencounterzerogenerateaninterruptSetupbeforeschedulingprocesstoregaincontrolorterminateprogramthatexceedsallottedtimeTimerTimertopreventinfiniteProcessManagementAprocessisaprograminexecution.Itisaunitofworkwithinthesystem.Programisapassiveentity,processisanactiveentity.ProcessneedsresourcestoaccomplishitstaskCPU,memory,I/O,filesInitializationdataProcessterminationrequiresreclaimofanyreusableresourcesSingle-threadedprocesshasoneprogramcounterspecifyinglocationofnextinstructiontoexecuteProcessexecutesinstructionssequentially,oneatatime,untilcompletionMulti-threadedprocesshasoneprogramcounterperthreadTypicallysystemhasmanyprocesses,someuser,someoperatingsystemrunningconcurrentlyononeormoreCPUsConcurrencybymultiplexingtheCPUsamongtheprocesses/threadsProcessManagementProcessManagementActivitiesTheoperatingsystemisresponsibleforthefollowingactivitiesinconnectionwithprocessmanagement:CreatinganddeletingbothuserandsystemprocessesSuspendingandresumingprocessesProvidingmechanismsforprocesssynchronizationProvidingmechanismsforprocesscommunicationProvidingmechanismsfordeadlockhandlingProcessManagementActivitiesTMemoryManagementAlldatainmemorybeforeandafterprocessingAllinstructionsinmemoryinordertoexecuteMemorymanagementdetermineswhatisinmemorywhenOptimizingCPUutilizationandcomputerresponsetousersMemorymanagementactivitiesKeepingtrackofwhichpartsofmemoryarecurrentlybeingusedandbywhomDecidingwhichprocesses(orpartsthereof)anddatatomoveintoandoutofmemoryAllocatinganddeallocatingmemoryspaceasneededMemoryManagementAlldatainmStorageManagementOSprovidesuniform,logicalviewofinformationstorageAbstractsphysicalpropertiestologicalstorageunit-fileEachmediumiscontrolledbydevice(i.e.,diskdrive,tapedrive)Varyingpropertiesincludeaccessspeed,capacity,data-transferrate,accessmethod(sequentialorrandom)File-SystemmanagementFilesusuallyorganizedintodirectoriesAccesscontrolonmostsystemstodeterminewhocanaccesswhatOSactivitiesincludeCreatinganddeletingfilesanddirectoriesPrimitivestomanipulatefilesanddirsMappingfilesontosecondarystorageBackupfilesontostable(non-volatile)storagemediaStorageManagementOSprovidesMass-StorageManagementUsuallydisksusedtostoredatathatdoesnotfitinmainmemoryordatathatmustbekeptfora“l(fā)ong”periodoftime.PropermanagementisofcentralimportanceEntirespeedofcomputeroperationhingesondisksubsystemanditsalgorithmsOSactivitiesFree-spacemanagementStorageallocationDiskschedulingSomestorageneednotbefastTertiarystorageincludesopticalstorage,magnetictapeStillmustbemanagedVariesbetweenWORM(write-once,read-many-times)a