Basic Memory Management Monoprogramming Protection Swapping Overlaying OS space User space.

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Presentation transcript:

Basic Memory Management Monoprogramming Protection Swapping Overlaying OS space User space

Multiprogramming with Fixed Partitions Placement External Fragmentation Protection Relocation

Variable Partition Allocation Protection Relocation Compaction Placement Strategies First fit Next fit Best fit Worst fit Quick fit Free Allocated Free Allocated

Variable Partition Allocation Memory Management with Bitmaps Memory Management with Linked Lists P/HStartsLengthPtr

Virtual Memory Memory Hierarchy Address Space Run-time Memory Logical Blocks - Segments Physical Blocks - Pages Primary memory Secondary memory

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.

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

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

Virtual Memory Protection Demand Paging Page Faults Expensive overhead Prepaging TLB – Translation Lookaside Buffer Cache of high-demand pages

Page Replacement Algorithms The Optimal Page Replacement Algorithm Least Recently Used Least Frequently Used First In First Out – FIFO

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

Design and Implementation Issues Page size Separate Instruction and Data Spaces Shared Pages Local versus Global Allocation Page Fault Handling Locking Pages in Memory

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

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)