Virtual Memory

Virtual Memory

1. Address Translation

   • Address Space Mapping
     • The components of a source program are represented using symbolic identifiers, labels and variables  all those things are elements of the program’s name space.

2. Segmentataion

   • Segmentation is an extension of the ideas suggested by the use of relocation-limit registers for relocating and bound-checking blocks of memory.
     • segmentNumber – identifies the particular logical block of the VM
     • Offset – linear offset from the beginning of the target segment

3. Paging

   • the unit of memory that is moved back and forth between primary and secondary memory is a page.
   • Static Paging Algorithm
     • Fetch policy – decides when a page should be loaded into PM
     • Replacement policy – determines which page should be removed from PM if all page frames are full
     • Placement policy – determines where the fetched page should be loaded in PM
   • Demand Paging Algorithms
     • Random placement
     • Belady’s Optimal Algorithm
     • Least Recently Used (LRU)
     • Least Frequently Used (LFU)
     • First In First Out (FIFO)
     • Stack Algorithm

4. Memory mapped files

   • the file manager essentially forwards all read() and write() operations to the VM manager.

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