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Chapter 8: Main Memory (Background (Protection (Need to ensure that a…
Chapter 8: Main Memory
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Paging
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Definition
a memory management mechanism that allows the physical address space of a process to be non-contagious.
physical memory is divided into blocks of equal size called Pages and they belong to a certain process are loaded into available memory frames.
Page table
data structure used by a virtual memory system in a computer operating system to store the mapping between virtual address and physical addresses.
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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
Type of swapping
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
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Background
Protection
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Protection by using a pair of base and limit registers define the logical address space of a process
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Fragmentation
External fragmentation
total memory space exists to satisfy a request, but it is not contiguous
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Internal fragmentation
allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used