Monday, March 17, 2014

Overlays

Overlays in Operating systems

          The entire program and data of a process must be in the physical memory for the process to execute. The size of a process is limited to the size of physical memory.
If a process is larger than the amount of memory, a technique called overlays can be used. Overlays is to keep in memory only those instructions and data that are needed at any given time. When other instructions are needed, they are loaded into space that was occupied previously by instructions that are no longer needed.

Overlays are
implemented by user; no special support needed from operating system, programming design of overlay structure is complex.

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