The Memory System-I

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1、SFTW230:SystemsandNetworksIComputerOrganizationTopicscovered:Chapter5.TheMemorySystem(I)Dr.WUWen,FST,UMOutlineßSomebasicconceptsßMemoryhierarchyßCachememoriesßSemiconductorRAMmemories15.1SomebasicconceptsßMaximumsizeofthememorydependsontheaddressingscheme:©16-bitcomputer

2、generates16-bitaddressesandcanaddressupto216=66536=64Kmemorylocations.©32-bitcomputergenerates32-bitaddressesandcanaddressupto232=4Gmemorylocations.210–1K=220–1M=–1G=230–1T=240©Mostmachinesbyteaddressablebutretrieve/storedatainwordsaboutonememoryaccess.2Somebasicconcepts

3、(cont.)ProcessorMemoryk-bitaddressbusMARn-bitdatabuskUpto2addressableMDRlocationsWordlength=nbitsControllines(,MFC,etc.)R/W•RecallthatthedatatransfersbetweenaprocessorandmemoryinvolvestworegistersMARandMDR.•MAR:kbitslong;MDR:nbitslong.Æmemoryunitbeupto2k.•Controllinesinc

4、ludeR/WandMemoryFunctionCompleted(MFC)Æcoordinatingdatatransfers.3Memoryhierarchy(5.4and5.5inTextbook)ßThememorystructureofacomputer©Multiplelevelsofmemorieswithdifferentspeedsandsizes.•Closertoprocessor,fasterandsmaller4MemoryhierarchyProcessor•ProcessorregistersFastest

5、accessistothedataheldinRegistersregistersareatthetopofthememoryhierarchy.IncreasingIncreasingIncreasingsizespeedcostperbit•ProcessorcachePrimaryL1Relativelysmallamountofmemorythatcachecanbeimplementedontheprocessorchip.•Twolevelsofcache.Level1(L1)cacheSecondaryisonthepro

6、cessorchip.Level2(L2)cacheL2cacheisinbetweenmainmemoryandprocessor.(earlierprocessorgeneration)•MainmemoryMainMuchlarger,butmuchslowerthancachememorymemory.•Magneticdisks.Hugeamountofinexpensivestorage.Magneticdisksecondarymemory5CacheMemoriesßCachememory©Anarchitectural

7、arrangementwhichmakesthemainmemoryappearfastertotheprocessorthanitreallyis.ßToreducetheexecutiontime©WeshouldimprovethepossibilityoffindingthecurrentexecutedinstructionsinthecacheHowTo?•AnalysistheprogramexecutionpatternDuringsomeperiodoftime,manyinstructionsinlocalizeda

8、reasofaprogramareexecutedmoreoftenthanothers.localityofreference6LocalityofreferenceßTwoforms:©Temporal