中山大学软件学院操作系统概念课件——ch1.ppt

Chapter1 Introduction Chapter1 Introduction WhatOperatingSystemsDoComputer SystemOrganizationComputer SystemArchitectureOperating SystemStructureOperating SystemOperationsProcessManagementMemoryManagementStorageManagementProtectionandSecurityDistributedSystemsSpecial PurposeSystemsComputingEnvironmentsOpen SourceOperatingSystems Objectives ToprovideagrandtourofthemajoroperatingsystemscomponentsToprovidecoverageofbasiccomputersystemorganization WhatisanOperatingSystem AprogramthatactsasanintermediarybetweenauserofacomputerandthecomputerhardwareOperatingsystemgoals ExecuteuserprogramsandmakesolvinguserproblemseasierMakethecomputersystemconvenienttouseUsethecomputerhardwareinanefficientmanner ComputerSystemStructure Computersystemcanbedividedintofourcomponents Hardware providesbasiccomputingresourcesCPU memory I OdevicesOperatingsystemControlsandcoordinatesuseofhardwareamongvariousapplicationsandusersApplicationprograms definethewaysinwhichthesystemresourcesareusedtosolvethecomputingproblemsoftheusersWordprocessors compilers webbrowsers databasesystems videogamesUsersPeople machines othercomputers FourComponentsofaComputerSystem WhatOperatingSystemsDo DependsonthepointofviewUserswantconvenience easeofuseDon tcareaboutresourceutilizationButsharedcomputersuchasmainframeorminicomputermustkeepallusershappyUsersofdedicatesystemssuchasworkstationshavededicatedresourcesbutfrequentlyusesharedresourcesfromserversHandheldcomputersareresourcepoor optimizedforusabilityandbatterylifeSomecomputershavelittleornouserinterface suchasembeddedcomputersindevicesandautomobiles OperatingSystemDefinition OSisaresourceallocatorManagesallresourcesDecidesbetweenconflictingrequestsforefficientandfairresourceuseOSisacontrolprogramControlsexecutionofprogramstopreventerrorsandimproperuseofthecomputer OperatingSystemDefinition Cont Nouniversallyaccepteddefinition Everythingavendorshipswhenyouorderanoperatingsystem isgoodapproximationButvarieswildly Theoneprogramrunningatalltimesonthecomputer isthekernel Everythingelseiseitherasystemprogram shipswiththeoperatingsystem oranapplicationprogram ComputerStartup bootstrapprogramisloadedatpower uporrebootTypicallystoredinROMorEPROM generallyknownasfirmwareInitializesallaspectsofsystemLoadsoperatingsystemkernelandstartsexecution ComputerSystemOrganization Computer systemoperationOneormoreCPUs devicecontrollersconnectthroughcommonbusprovidingaccesstosharedmemoryConcurrentexecutionofCPUsanddevicescompetingformemorycycles Computer SystemOperation I OdevicesandtheCPUcanexecuteconcurrentlyEachdevicecontrollerisinchargeofaparticulardevicetypeEachdevicecontrollerhasalocalbufferCPUmovesdatafrom tomainmemoryto fromlocalbuffersI OisfromthedevicetolocalbufferofcontrollerDevicecontrollerinformsCPUthatithasfinisheditsoperationbycausinganinterrupt CommonFunctionsofInterrupts Interrupttransferscontroltotheinterruptserviceroutinegenerally throughtheinterruptvector whichcontainstheaddressesofalltheserviceroutinesInterruptarchitecturemustsavetheaddressoftheinterruptedinstructionIncominginterruptsaredisabledwhileanotherinterruptisbeingprocessedtopreventalostinterruptAtrapisasoftware generatedinterruptcausedeitherbyanerrororauserrequestAnoperatingsystemisinterruptdriven InterruptHandling TheoperatingsystempreservesthestateoftheCPUbystoringregistersandtheprogramcounterDetermineswhichtypeofinterrupthasoccurred pollingvectoredinterruptsystemSeparatesegmentsofcodedeterminewhatactionshouldbetakenforeachtypeofinterrupt InterruptTimeline I OStructure AfterI Ostarts controlreturnstouserprogramonlyuponI OcompletionWaitinstructionidlestheCPUuntilthenextinterruptWaitloop contentionformemoryaccess AtmostoneI Orequestisoutstandingatatime nosimultaneousI OprocessingAfterI Ostarts controlreturnstouserprogramwithoutwaitingforI OcompletionSystemcall requesttotheoperatingsystemtoallowusertowaitforI OcompletionDevice statustablecontainsentryforeachI Odeviceindicatingitstype address andstateOperatingsystemindexesintoI Odevicetabletodeterminedevicestatusandtomodifytableentrytoincludeinterrupt DirectMemoryAccessStructure Usedforhigh speedI OdevicesabletotransmitinformationatclosetomemoryspeedsDevicecontrollertransfersblocksofdatafrombufferstoragedirectlytomainmemorywithoutCPUinterventionOnlyoneinterruptisgeneratedperblock ratherthantheoneinterruptperbyte StorageStructure Mainmemory onlylargestoragemediathattheCPUcanaccessdirectlyRandomaccessTypicallyvolatileSecondarystorage extensionofmainmemorythatprovideslargenonvolatilestoragecapacityMagneticdisks rigidmetalorglassplatterscoveredwithmagneticrecordingmaterialDisksurfaceislogicallydividedintotracks whicharesubdividedintosectorsThediskcontrollerdeterminesthelogicalinteractionbetweenthedeviceandthecomputer StorageHierarchy StoragesystemsorganizedinhierarchySpeedCostVolatilityCaching copyinginformationintofasterstoragesystem mainmemorycanbeviewedasacacheforsecondarystorage Storage DeviceHierarchy Caching Importantprinciple performedatmanylevelsinacomputer inhardware operatingsystem software InformationinusecopiedfromslowertofasterstoragetemporarilyFasterstorage cache checkedfirsttodetermineifinformationisthereIfitis informationuseddirectlyfromthecache fast Ifnot datacopiedtocacheandusedthereCachesmallerthanstoragebeingcachedCachemanagementimportantdesignproblemCachesizeandreplacementpolicy Computer SystemArchitecture Mostsystemsuseasinglegeneral purposeprocessor PDAsthroughmainframes Mostsystemshavespecial purposeprocessorsaswellMultiprocessorssystemsgrowinginuseandimportanceAlsoknownasparallelsystems tightly coupledsystemsAdvantagesinclude IncreasedthroughputEconomyofscaleIncreasedreliability gracefuldegradationorfaulttoleranceTwotypes AsymmetricMultiprocessingSymmetricMultiprocessing HowaModernComputerWorks AvonNeumannarchitecture SymmetricMultiprocessingArchitecture ADual CoreDesign ClusteredSystems Likemultiprocessorsystems butmultiplesystemsworkingtogetherUsuallysharingstorageviaastorage areanetwork SAN Providesahigh availabilityservicewhichsurvivesfailuresAsymmetricclusteringhasonemachineinhot standbymodeSymmetricclusteringhasmultiplenodesrunningapplications monitoringeachotherSomeclustersareforhigh performancecomputing HPC Applicationsmustbewrittentouseparallelization ClusteredSystems OperatingSystemStructure MultiprogrammingneededforefficiencySingleusercannotkeepCPUandI OdevicesbusyatalltimesMultiprogrammingorganizesjobs codeanddata soCPUalwayshasonetoexecuteAsubsetoftotaljobsinsystemiskeptinmemoryOnejobselectedandrunviajobschedulingWhenithastowait forI Oforexample OSswitchestoanotherjobTimesharing multitasking islogicalextensioninwhichCPUswitchesjobssofrequentlythatuserscaninteractwitheachjobwhileitisrunning creatinginteractivecomputingResponsetimeshouldbe 1secondEachuserhasatleastoneprogramexecutinginmemory processIfseveraljobsreadytorunatthesametime CPUschedulingIfprocessesdon tfitinmemory swappingmovestheminandouttorunVirtualmemoryallowsexecutionofprocessesnotcompletelyinmemory MemoryLayoutforMultiprogrammedSystem Operating SystemOperations InterruptdrivenbyhardwareSoftwareerrororrequestcreatesexceptionortrapDivisionbyzero requestforoperatingsystemserviceOtherprocessproblemsincludeinfiniteloop processesmodifyingeachotherortheoperatingsystemDual modeoperationallowsOStoprotectitselfandothersystemcomponentsUsermodeandkernelmodeModebitprovidedbyhardwareProvidesabilitytodistinguishwhensystemisrunningusercodeorkernelcodeSomeinstructionsdesignatedasprivileged onlyexecutableinkernelmodeSystemcallchangesmodetokernel returnfromcallresetsittouser TransitionfromUsertoKernelMode Timertopreventinfiniteloop processhoggingresourcesSetinterruptafterspecificperiodOperatingsystemdecrementscounterWhencounterzerogenerateaninterruptSetupbeforeschedulingprocesstoregaincontrolorterminateprogramthatexceedsallottedtime ProcessManagement Aprocessisaprograminexecution Itisaunitofworkwithinthesystem Programisapassiveentity processisanactiveentity ProcessneedsresourcestoaccomplishitstaskCPU memory I O filesInitializationdataProcessterminationrequiresreclaimofanyreusableresourcesSingle threadedprocesshasoneprogramcounterspecifyinglocationofnextinstructiontoexecuteProcessexecutesinstructionssequentially oneatatime untilcompletionMulti threadedprocesshasoneprogramcounterperthreadTypicallysystemhasmanyprocesses someuser someoperatingsystemrunningconcurrentlyononeormoreCPUsConcurrencybymultiplexingtheCPUsamongtheprocesses threads ProcessManagementActivities CreatinganddeletingbothuserandsystemprocessesSuspendingandresumingprocessesProvidingmechanismsforprocesssynchronizationProvidingmechanismsforprocesscommunicationProvidingmechanismsfordeadlockhandling Theoperatingsystemisresponsibleforthefollowingactivitiesinconnectionwithprocessmanagement MemoryManagement AlldatainmemorybeforeandafterprocessingAllinstructionsinmemoryinordertoexecuteMemorymanagementdetermineswhatisinmemorywhenOptimizingCPUutilizationandcomputerresponsetousersMemorymanagementactivitiesKeepingtrackofwhichpartsofmemoryarecurrentlybeingusedandbywhomDecidingwhichprocesses orpartsthereof anddatatomoveintoandoutofmemoryAllocatinganddeallocatingmemoryspaceasneeded StorageManagement OSprovidesuniform logicalviewofinformationstorageAbstractsphysicalpropertiestologicalstorageunit fileEachmediumiscontrolledbydevice i e diskdrive tapedrive Varyingpropertiesincludeaccessspeed capacity data transferrate accessmethod sequentialorrandom File SystemmanagementFilesusuallyorganizedintodirectoriesAccesscontrolonmostsystemstodeterminewhocanaccesswhatOSactivitiesincludeCreatinganddeletingfilesanddirectoriesPrimitivestomanipulatefilesanddirsMappingfilesontosecondarystorageBackupfilesontostable non volatile storagemedia Mass StorageManagement Usuallydisksusedtostoredatathatdoesnotfitinmainmemoryordatathatmustbekeptfora long periodoftimePropermanagementisofcentralimportanceEntirespeedofcomputeroperationhingesondisksubsystemanditsalgorithmsOSactivitiesFree spacemanagementStorageallocationDiskschedulingSomestorageneednotbefastTertiarystorageincludesopticalstorage magnetictapeStillmustbemanaged byOSorapplicationsVariesbetweenWORM write once read many times andRW read write PerformanceofVariousLevelsofStorage Movementbetweenlevelsofstoragehierarchycanbeexplicitorimplicit MigrationofIntegerAfromDisktoRegister Multitaskingenvironmentsmustbecarefultousemostrecentvalue nomatterwhereitisstoredinthestoragehierarchyMultiprocessorenvironmentmustprovidecachecoherencyinhardwaresuchthatallCPUshavethemostrecentvalueintheircacheDistributedenvironmentsituationevenmorecomplexSeveralcopiesofadatumcanexistVarioussolutionscoveredinChapter17 I OSubsystem OnepurposeofOSistohidepeculiaritiesofhardwaredevicesfromtheuserI OsubsystemresponsibleforMemorymanagementofI Oincludingbuffering storingdatatemporarilywhileitisbeingtransferred caching storingpartsofdatainfasterstorageforperformance spooling theoverlappingofoutputofonejobwithinputofotherjobs Generaldevice driverinterfaceDriversforspecifichardwaredevices ProtectionandSecurity Protection anymechanismforcontrollingaccessofprocessesoruserstoresourcesdefinedbytheOSSecurity defenseofthesystemagainstinternalandexternalattacksHugerange includingdenial of service worms viruses identitytheft theftofserviceSystemsgenerallyfirstdistinguishamongusers todeterminewhocandowhatUseridentities userIDs securityIDs includenameandassociatednumber oneperuserUserIDthenassociatedwithallfiles processesofthatusertodetermineaccesscontrolGroupidentifier groupID allowssetofuserstobedefinedandcontrolsmanaged thenalsoassociatedwitheachprocess filePrivilegeescalationallowsusertochangetoeffectiveIDwithmorerights DistributedComputing Collectionofseparate possiblyheterogeneous systemsnetworkedtogetherNetworkisacommunicationspathLocalAreaNetwork LAN WideAreaNetwork WAN MetropolitanAreaNetwork MAN NetworkOperatingSystemprovidesfeaturesbetweensystemsacrossnetworkCommunicationschemeallowssystemstoexchangemessagesIllusionofasinglesystem Special PurposeSystems Real timeembeddedsystemsmostprevalentformofcomputersVaryconsiderable specialpurpose limitedpurposeOS real timeOSMultimediasystemsStreamsofdatamustbedeliveredaccordingtotimerestrictionsHandheldsystemsPDAs smartphones limitedCPU memory powerReducedfeaturesetOS limitedI O ComputingEnvironments TraditionalcomputerBlurringovertimeOfficeenvironmentPCsconnectedtoanetwork terminalsattachedtomainframeorminicomputersprovidingbatchandtimesha