操作系统原理与设计第8章MainMemory3陈香兰中国科学技术大学计算机学院2009年11月17日......提纲Segmentation(分段)BasicMethodHardwareSegmentationwithpagingExample:TheIntelPentium小结和作业......DiscreteMemoryAllocationIpaging（分页）Iinternalfragmentation<onepageIsegmentation（分段）IlogicalIcombinedpaging＆segmentation（段页式）......OutlineSegmentation(分段)BasicMethodHardwareSegmentationwithpagingExample:TheIntelPentium小结和作业......SegmentationISegmentation:supportinguserviewofmemoryIAprogramisacollectionofsegments.User’sViewofaProgramAsegmentisalogicalunitsuchas:mainprogram,procedure,function,method,object,localvariables,globalvariables,commonblock,stack,symboltable,arrays......LogicaladdressspaceIAcollectionofsegmentsIeachsegment<name;length>I2-DaddressspaceIAlogicaladdressconsistsofatwotupleI<seg−name;offset>,orI<seg−num;offset>ICompilerautomaticallyconstructssegmentsreflectingtheinputprogram.IPascalcompilerIFORTRANcompilerICcompiler,suchasgcc,:::......LogicalViewofSegmentation......OutlineSegmentation(分段)BasicMethodHardwareSegmentationwithpagingExample:TheIntelPentium小结和作业......SegmentationArchitectureIISegmenttable–maps2-DLA!1-DPA;eachtableentryhas:Ibase–containsthestartingphysicaladdresswherethesegmentsresideinmemoryIlimit–specifiesthelengthofthesegmentISegment-tablebaseregister(STBR)pointstothesegmenttable’slocationinmemoryISegment-tablelengthregister(STLR)indicatesnumberofsegmentsusedbyaprogram;segmentnumbersislegalifs<STLR......SegmentationArchitectureII......SegmentationArchitectureIIIIProtectionIWitheachentryinsegmenttableassociate:Ivalidationbit=0)illegalsegmentIread/write/executeprivilegesIProtectionbitsassociatedwithsegments;codesharingoccursatsegmentlevelISincesegmentsvaryinlength,memoryallocationisadynamicstorage-allocationproblemIFirst-fit,Best-fit,:::IExternelfragmentation,compaction,:::......ExampleofSegmentationI<segment2;53>!4300+53=4353I<setment3;852>!3200+8