操作系统教学课件：Chapter 2 Computer-System Structures

Chapter2:Computer-SystemStructures从OS的角度看计算机系统的结构，每个部件都有一个软件部分（controller）为了管理和应用计算机资源，OS自身应该包括哪些组件ComputerSystemOperationI/OStructureStorageStructureStorageHierarchyHardwareProtectionGeneralSystemArchitectureOSsystemcomponentsComputer-SystemArchitectureComputer-SystemArchitecture指令系统Computer-SystemOperationI/OdevicesandtheCPUcanexecuteconcurrently.Eachdevicecontrollerisinchargeofaparticulardevicetype.Eachdevicecontrollerhasalocalbuffer（缓存）.CPUmovesdatafrom/tomainmemoryto/fromlocalbuffersI/Oisfromthedevicetolocalbufferofcontroller.DevicecontrollerinformsCPUthatithasfinisheditsoperationbycausinganinterrupt.CommonFunctionsofInterruptsInterrupt

（中断）transferscontroltotheinterruptserviceroutinegenerally,throughtheinterruptvector,whichcontainstheaddressesofalltheserviceroutines.Interruptarchitecturemustsavetheaddressoftheinterruptedinstruction.Incominginterruptsaredisabledwhileanotherinterruptisbeingprocessedtopreventalostinterrupt.A

trap

（陷阱）isasoftware-generatedinterruptcausedeitherbyanerrororauserrequest.Anoperatingsystemisinterruptdriven.（操作系统的运行是一种中断驱动机制）

OS

Application

&

user

hardwareOS启动后，设置好环境，设置好trap和interrupt。然后自顾自地运行有事call

OS有事发interruptInterruptHandlingTheoperatingsystempreservesthestateoftheCPUbystoringregistersandtheprogramcounter（PC）.Determineswhichtypeofinterrupthasoccurred:polling（轮询）vectoredinterruptsystemSeparatesegmentsofcodedeterminewhatactionshouldbetakenforeachtypeofinterruptInterruptTimeLineForaSingleProcessDoingOutputInterruptTimeLineForaSingleProcessDoingOutput产生中断产生中断InterruptTimeLineForaSingleProcessDoingOutput产生中断产生中断中断处理中断处理I/OStructureAfterI/Ostarts,controlreturnstouserprogramonlyuponI/Ocompletion.–

synchronous同步WaitinstructionidlestheCPUuntilthenextinterruptWaitloop(contentionformemoryaccess).AtmostoneI/Orequestisoutstandingatatime,nosimultaneousI/Oprocessing.AfterI/Ostarts,controlreturnstouserprogramwithoutwaitingforI/Ocompletion.–

asynchronous异步Systemcall

–requesttotheoperatingsystemtoallowusertowaitforI/Ocompletion.Device-statustablecontainsentryforeachI/Odeviceindicatingitstype,address,andstate.OperatingsystemindexesintoI/Odevicetabletodeterminedevicestatusandtomodifytableentrytoincludeinterrupt.TwoI/OMethodsSynchronousAsynchronousDevice-StatusTableThetablecontaininganentryforeachI/Odevice,eachentryindicatesthedevice’stype,address,stateDirectMemoryAccessStructureUsedforhigh-speedI/Odevicesabletotransmitinformationatclosetomemoryspeeds.DevicecontrollertransfersblocksofdatafrombufferstoragedirectlytomainmemorywithoutCPUintervention.Onlyoninterruptisgeneratedperblock,ratherthantheoneinterruptperbyte.StorageStructureMainmemory–onlylargestoragemediathattheCPUcanaccessdirectly.Secondarystorage–extensionofmainmemorythatprovideslargenonvolatilestoragecapacity.Magneticdisks–rigidmetalorglassplatterscoveredwithmagneticrecordingmaterialDisksurfaceislogicallydividedintotracks,whicharesubdividedintosectors.Thediskcontrollerdeterminesthelogicalinteractionbetweenthedeviceandthecomputer.Moving-HeadDiskMechanismMoving-HeadDiskMechanism存储容量＝磁头数×磁道（柱面）数×每道扇区数×每扇区字节数

要点：（1）硬盘有数个盘片，每盘片两个面，每个面一个磁头

（2）盘片被划分为多个扇形区域即扇区

（3）同一盘片不同半径的同心圆为磁道

（4）不同盘片相同半径构成的圆柱面即柱面

（5）信息记录可表示为：××磁道（柱面），××磁头，××扇区StorageHierarchy希望速度越快越好、价格越低越好、信息不要丢失Storagesystemsorganizedinhierarchy.SpeedCostVolatilityCaching

–copyinginformationintofasterstoragesystem;mainmemorycanbeviewedasalastcacheforsecondarystorage.Storage-DeviceHierarchy最贵CPU级几十个易失纳秒级M易失微秒级M、G毫秒级G不易失秒级T不易失CachingUseofhigh-speedmemorytoholdrecently-accesseddata.Requiresacachemanagementpolicy.Cachingintroducesanotherlevelinstoragehierarchy.Thisrequiresdatathatissimultaneouslystoredinmorethanoneleveltobeconsistent(一致性).MigrationofAFromDisktoRegisterCachecoherencyandconsistencyHardwareProtection为什么要保护？-保护的目的是让硬件公平、高效地为当前所有用户服务，不是保护起来不让用户使用保护哪些？-硬件资源怎么保护？-依赖于硬件Dual-ModeOperationI/OProtectionMemoryProtectionCPUProtectionDual-ModeOperation特权与普权Sharingsystemresourcesrequiresoperatingsystemtoensurethatanincorrectprogramcannotcauseotherprogramstoexecuteincorrectly.Providehardwaresupporttodifferentiatebetweenatleasttwomodesofoperations.1. Usermode（用户态、目态）

–executiondoneonbehalfofauser.2.

Monitormode（管态、内核态）

(alsokernelmodeorsystemmode)–executiondoneonbehalfofoperatingsystem.Dual-ModeOperation(Cont.)Modebitaddedtocomputerhardwaretoindicatethecurrentmode:monitor(0)oruser(1).Whenaninterruptorfaultoccurshardwareswitchestomonitormode.Privilegedinstructions

canbeissuedonlyinmonitormode.monitoruserInterrupt/faultsetusermodeI/OProtection-由OS掌控AllI/Oinstructionsareprivilegedinstructions.Mustensurethatauserprogramcouldnevergaincontrolofthecomputerinmonitormode(I.e.,auserprogramthat,aspartofitsexecution,storesanewaddressintheinterruptvector).UseofASystemCalltoPerformI/OMemoryProtection-OS确定私人空间Mustprovidememoryprotectionatleastfortheinterruptvectorandtheinterruptserviceroutines.Inordertohavememoryprotection,addtworegistersthatdeterminetherangeoflegaladdressesaprogrammayaccess:Baseregister

–holdsthesmallestlegalphysicalmemoryaddress.Limitregister

–containsthesizeoftherangeMemoryoutsidethedefinedrangeisprotected.UseofABaseandLimitRegisterHardwareAddressProtectionHardwareProtectionWhenexecutinginmonitormode,theoperatingsystemhasunrestrictedaccesstobothmonitoranduser’smemory.Theloadinstructionsforthebaseandlimitregistersareprivilegedinstructions.CPUProtection-工作与休息Timer（定时器）

–interruptscomputerafterspecifiedperiodtoensureoperatingsystemmaintainscontrol.Timerisdecrementedeveryclocktick.Whentimerreachesthevalue0,aninterruptoccurs.Timercommonlyusedtoimplementtimesharing.Timealsousedtocomputethecurrenttime.Load-timerisaprivilegedinstruction.NetworkStructureLocalAreaNetworks(LAN)WideAreaNetworks(WAN)LocalAreaNetworkStructureWideAreaNetworkStructureOSsystemcomponentsCPU-ProcessmanagementMemory-Main-memorymanagementDisk-FilemanagementStoragesystem-Secondary-storagemanagementI/O-I/O-systemmanagement不同计算机连起来

-Networking保护和安全

-Protectionsystem计算机为人所用

-Userinterfacesystemsummary从OS角度看计算机系统硬件保护双模态、定时器OS自身的系统组件作业1.Howdoesthedistinctionbetweenmonitormodeandusermodefunctionasarudimentaryformofprotection(security)system?2.

Whatarethedifferencesbetweenatrapandaninterrupt?Whatistheuseofeachfunction?3.Whichofthefol