操作系統(tǒng)概念-老師移動學(xué)院ch8s

Chapter8:MemoryContiguousMemoryStructureofthePageOperatingSystemConcepts–7thEdition,Feb22,

Toprovideadetaileddescriptionofvariouswaysoforganizingmemoryhardware techniques,includingpagingandsegmentationOperatingSystemConcepts–7thEdition,Feb22,

Programmustbebrought(fromdisk)intomemoryandplacedaprocessforittobeMainmemoryandregistersareonlystorageCPUcanaccessRegisteraccessinoneCPUclock(orMainmemorycantakemanyCachesitsbetweenmainmemoryandCPUProtectionofmemoryrequiredtoensurecorrectOperatingSystemConcepts–7thEdition,Feb22,

BaseandLimitApairofbaseandlimitregistersdefinethelogicaladdressspaceOperatingSystemConcepts–7thEdition,Feb22,

TheconceptofalogicaladdressspacethatisboundtoamemorymanagementPhysicaladdress–addressseenbythememoryLogicalandphysicaladdressesarethesameincompile-timeandload-timeaddress-bindingschemes;logical(virtual)andphysicaladdressesdifferinexecution-timeaddress-bindingOperatingSystemConcepts–7thEdition,Feb22,

Memory-ManagementUnitHardwaredevicethatmapsvirtualtophysicalInMMUscheme,thevalueintherelocationregisterisaddedtoeveryaddressgeneratedbyauserprocessatthetimeitissenttomemoryTheuserprogramdealswithlogicaladdresses;itneverseestherealphysicaladdressesOperatingSystemConcepts–7thEdition,Feb22,

HWaddressprotectionwithbaseandlimitOperatingSystemConcepts–7thEdition,Feb22,

ContiguousMainmemoryusuallyintotwoResidentoperatingsystem,usuallyheldinlowmemoryinterruptUserprocessesthenheldinhighRelocationregistersusedtoprotectuserprocessesfromother,andfromchangingoperating-systemcodeandBaseregistercontainsvalueofsmallestphysicalLimitregistercontainsrangeoflogicaladdresses–eachlogicaladdressmustbelessthanthelimitregisterMMUmapslogicaladdressOperatingSystemConcepts–7thEdition,Feb22,

ContiguousAllocationMultiple-partitionHole–blockofavailablememory;holesofvarioussizescatteredthroughoutWhenaprocessarrives,itisallocatedmemoryfromaholeenough modateOperatingsystemmaintainsinformationa)allocated processOperatingSystemConcepts–7thEdition,Feb22,

DynamicStorage-AllocationHowtosatisfyarequestofsizenfromalistoffreeFirst-fit:Allocatethefirstholethatisbigsearchentirelist,unlessorderedbyFirst-fitandbest-fitbetterthanworst-fitintermsofandstorageOperatingSystemConcepts–7thEdition,Feb22,

satisfyarequest,butitisnotlargerthanrequestedmemory;thissizedifferenceismemoryinternaltoapartition,butnotbeingusedReduceexternalfragmentationbyShufflememorycontentstoplaceallfreememorytogetherinlargeCompactionispossibleonlyifrelocationisdynamic,andisatexecutionOperatingSystemConcepts–7thEdition,Feb22,

大小不等的固定分區(qū)和大小可變的分區(qū)效率低下，會產(chǎn)生內(nèi)部或外部碎片。若將主存劃分為固定大小塊，并且塊較小，每個(gè)進(jìn)程也被分為同樣大小的小塊，可以將進(jìn)程的塊（稱為頁）指定到內(nèi)存中的可用塊（稱為幀或頁幀，最后一頁可能形成內(nèi)部碎片，沒有外部碎片OperatingSystemConcepts–7thEdition,Feb22,

OperatingSystemConcepts–7thEdition,Feb22,

頁OperatingSystemConcepts–7thEdition,Feb22,

Logicaladdressspaceofaprocesscanbenoncontiguous;processisallocatedphysicalmemorywheneverthelatterisDividephysicalmemoryintofixed-sizedblockscalled(sizeispowerof2,between512bytesand8,192DividelogicalmemoryintoblocksofsamesizecalledKeeptrackofallfreeTorunaprogramofsizenpages,needtofindnfreeframesandloadprogramSetupapagetabletotranslatelogicaltophysicalInternalOperatingSystemConcepts–7thEdition,Feb22,

PagingOperatingSystemConcepts–7thEdition,Feb22,

PagingModelofLogicalandPhysicalOperatingSystemConcepts–7thEdition,Feb22,

FreeBefore AfterOperatingSystemConcepts–7thEdition,Feb22,

Paging32-bytememoryand4-byteOperatingSystemConcepts–7thEdition,Feb22,

ImplementationofPageaccesses.OneforthepagetableandonefortheThetwomemoryaccessproblemcanbesolvedbytheuseofaspecialuniquelyidentifieseachprocesstoprovideaddress-spaceprotectionforthatprocessOperatingSystemConcepts–7thEdition,Feb22,

AssociativeAssociativememory–parallelPage FrameAddresstranslation(p,lIfpisinassociativeregister,getframe#lOtherwisegetframe#frompagetableinOperatingSystemConcepts–7thEdition,Feb22,

PagingHardwareWithOperatingSystemConcepts–7thEdition,Feb22,

AssociativeLookup=timeAssumememorycycletimeis1Hitratio–percentageoftimesthatapagenumberisfoundintheassociativeregisters;ratiorelatedtonumberofassociativeregistersHitratio=EAT=(1+)+(2+)(1–=2+–OperatingSystemConcepts–7thEdition,Feb22,

MemoryMemoryprotectionimplementedbyassociatingprotectionbitwitheachframel“valid”indicatesthattheassociatedpageisintheprocess’logicaladdressspace,andisthusalegall“invalid”indicatesthatthepageisnotinthelogicaladdressOperatingSystemConcepts–7thEdition,Feb22,

Valid(v)orInvalid(i)BitInAPageOperatingSystemConcepts–7thEdition,Feb22,

SharedOnecopyofread-only(reentrant)codesharedprocesses(i.e.,texteditors,compilers,windowSharedcodemustappearinsamelocationintheaddressspaceofallEachprocesskeepsaseparatecopyofthecodeandThepagesfortheprivatecodeanddatacanappearanywhereinthelogicaladdressspaceOperatingSystemConcepts–7thEdition,Feb22,

SharedPages

andGagneAprogramisacollectionofsegments.Asegmentisalogicalsuchmainprogram,localvariables,globalvariables,commonblock,symboltable,OperatingSystemConcepts–7thEdition,Feb22,

LogicalViewof4343213241user physicalmemoryOperatingSystemConcepts–7thEdition,Feb22,

程序和相關(guān)的數(shù)據(jù)被劃分成一組段（segment）分段技術(shù)的邏輯地址由兩部分組成：段號和偏移量由于使用大小不等的段，分段類似于動態(tài)分區(qū)。與動態(tài)分區(qū)不，在分段方案中，。分段消除了內(nèi)部碎片，但是和動態(tài)分區(qū)一樣，會產(chǎn)生很多外部碎片由于進(jìn)程被分為許多小塊，外部碎片較小OperatingSystemConcepts–7thEdition,Feb22,

一般情況上圖中，段長度=4，偏移量=12。最大段長度OperatingSystemConcepts–7thEdition,Feb22,

SegmentationLogicaladdressconsistsofatwo<segment-number,Segmenttable–mapstwo-dimensionalphysicaladdresses;tableentrylbase–containsthestartingphysicaladdresswheresegmentsresideinllimit–specifiesthelengthofthelocationinmemoryusedbyaprogram;segmentnumbersislegalifs<Op