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Published byJulia Poppy Modified over 10 years ago
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Basic Memory Management Monoprogramming Protection Swapping Overlaying OS space User space
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Multiprogramming with Fixed Partitions Placement External Fragmentation Protection Relocation
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Variable Partition Allocation Protection Relocation Compaction Placement Strategies First fit Next fit Best fit Worst fit Quick fit Free Allocated Free Allocated
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Variable Partition Allocation Memory Management with Bitmaps Memory Management with Linked Lists 1 1 0 0 0 1 1 1 0 0 0 0 1 1 1 0 1 0 1 1 0 0 1 1 1 1 0 0 0 1 1 1 1 1 1 1 1 0 0 0 1 1 1 0 0 1 1 1 P/HStartsLengthPtr
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Virtual Memory Memory Hierarchy Address Space Run-time Memory Logical Blocks - Segments Physical Blocks - Pages Primary memory Secondary memory
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Virtual Memory Paging Fixed size blocks 2-dim address Mapping and address translation Virtual to Physical (v.page no., byte no.) (p.page no., byte no.) PM SM Page no.Byte no.
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Virtual Memory Page Tables Logically one per process No. of rows equal no. of pages No. of columns determined by no. of entries (data fields per page) L/NL, M/NM, Page no., SSA, etc. Address translation Active PT, MMU, PTAR
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Virtual Memory Address translation Active PT, MMU, PTAR L/ NL M/ NM Page no. SSA 11200xxx 0yyy 10128zzz 4000 PTAR VA: (2, 596) PA: (128, 596) PT 4000 + 2
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Virtual Memory Protection Demand Paging Page Faults Expensive overhead Prepaging TLB – Translation Lookaside Buffer Cache of high-demand pages
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Page Replacement Algorithms The Optimal Page Replacement Algorithm Least Recently Used Least Frequently Used First In First Out – FIFO
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Page Replacement Algorithms Second Chance Check referenced bit Clock Circular list with referenced bit Not Recently Used Check referenced and modified bits 4 classes of pages The Working Set The WSClock
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Design and Implementation Issues Page size Separate Instruction and Data Spaces Shared Pages Local versus Global Allocation Page Fault Handling Locking Pages in Memory
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Segmentation Process divided into logical blocks – segments 2 dim addressing (s.no., byte no) – virtual address Segment Map Table (SMT) is required Variable partition allocation Address Translation VA: (s.no., byte) PA: (partition begin addr., byte) SMTAR Active SMT
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Segmentation with Paging Process divided into segments Segments divided into pages Memory allocated as pages VA: (s.no., page no., byte) PA: (page frame no., byte)
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