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34-One-level storage system.pdf

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34-One-level storage system.pdf

ComputerScience261Copyright2005Page1of3OneLevelStorageSystemKilburn,Edwards,Lanigan,Sumner1961SupersetofDynamicStorageAllocationintheAtlasComputer,IncludinganAutomaticUseofBackingStore,Fotheringham1961.WhatkindofpaperNewidea.Motivation.Explanation.Algorithms.AtlasArchitecture87bitFPaccumulator.12824bitindexregisters90availableforgeneraluse.ExecutivestoreincludesROMforSupervisor.48bitword24bithalfwords10bitopcode7bit7bitindexregisters24bitstoreaddresscharacteroffsettopbitidshalfwordop0mainmemory1executivestoreComputerScience261Copyright2005Page2of3MemoryArrangement512byteblocks/pages.OnePageAddressRegisterperinmemorycorepage.PARcontainstheaddressofthepagecurrentlyresidentinmemory.Priorityschemeofhandlingtapeanddrum.Firstdrum4usec.Nexttape11usec.Restoftimegoestocorestore.Memoryisbankedinto4stacks.MotivationforsinglelevelstoreTooexpensivetomakeentirememorycorestore.Tooslowtomakeentirememorydrum.Desireperformanceofcoreatcostofdrum.ImplementationofsinglelevelstoreFullyassociativelookuponeveryaddresslikeaTLBhowlargeistheirlookup32entrieswhywouldntthatworktoday.IfaddressfoundinaPAR,thenthedataisreturned.IfnoPARmatch,generateinterrupt.Keeptrackofdrumpositionintermsofblock.diskanalogyUseaWAFLalgorithmtoassignblockstodrum.keepdirectoryinmemory.BlockaddressgoesinPARuntildrumiscorrectlypositionedtopreventtransfertowrongblock.ComputerScience261Copyright2005Page3of3LearningprogramFirstuseofusebits.Oneusebitperpage.Canperformtransfersmemorytodrumdrumtomemoryineitherorderifyouleaveroomonbothmedia.Lockoutbitpreventsprogramsfromaccessingblocksthatarebeingtransferred.Pagereplacementusepasttopredictfuture.Periodicallyreadallusebitsandstorethemresetusebitsto0.periodicallyonceevery1024instructionswhynotrealtimethismakesitindependentofworkloadCalculatetandT,lengthsofthelasttwointervalsofinactivity.ApplyfollowingalgorithmIftisT1,useitimplicationisthatthepageisbeingusedlessfrequentlythaninthepast.PickpagewiththemaximumTtsuchthatt0heretheassumptionisthatthememorywillhavesimilarlengthidlestimes,sowearepickingthepagethathasthelargestamountofitsidletimeyettogo.PickmaximumTalltmustbe0principlehereisthateverythingisbusyandwellpickapagesuchthatwepromisewewontevictitagainifitwasamistake.Forallblocksondrum,calculatetauwhichisthetimeoflastuse.Whenmovingpagefromdrumtomemory,setTtobeidletimesincelastusecurrenttime–tautgetssetto0.ArgumentswhyAtlasprovidesflexibilityCanspreadthingsoutintheaddressspacetoallowforgrowth.Programscanmovebetweenmachineswithdifferentmemorysizeseasily.Onlystorageallocationaprogrammerneedstothinkaboutisallocatingdatatopages.

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