Memory management in the Operating System
The very important task of an OperatingSystem of providing the impression to each running application, that it has essentially unlimited linear memory at its disposal, when there is in fact only some 640KB, 16MB, 4GB plus possibly VirtualMemory? on the HardDisk? present.
Some ways to accomplish this include:
use a "memory management unit" (MMU) to bounds-check (in hardware) addresses not currently swapped into real RAM
On systems that don't have a MMU, emulate it by bounds-checking (in software) addresses that might not be currently swapped into real RAM.