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chap. 8 Main Memory (Paging (Physical address space of a process can be…
chap. 8 Main Memory
Paging
- Divide physical memory into fixed-sized blocks called frames
- Divide logical memory into blocks of same size called pages
- keep all track of all free frames
- Set up a page table to translate logical to physical addresses
- Backing store likewise split into pages
- Physical address space of a process can be noncontiguous; process is allocated physical memory whenever the latter is available
- Avoids external fragmentation
- Avoids problem of varying sized memory chunks.
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Swapping
- A process can be swapped temporarily out of memory to a backing store, and then brought back into memory for continued execution
- Backing store (fast disk large enough to accommodate copies of all memory images for all users; must provide direct access to these memory images)
* Roll out, roll in (swapping variant used for priority-based scheduling algorithms; lower-priority process is swapped out so higher-priority process can be loaded and executed)
- System maintains a ready queue of ready-to-run processes which have memory images on disk