Swapping

Swapping is the term for moving the contents of a process' address space, as a unitary entity, back and forth between main memory and secondary storage, when there are more processes active than can be accomodated simultaneously in main memory.

For a number of reasons, it has largely been superseded by paging, the most important of which being that the smallish fixed size of pages, and the ability to scatter the pages of a process, with them not needing to be contiguous, makes the allocation of physical memory much simpler in paging.

Swapping of a sort may still be used in some operating system, in that a process which has gone inactive may have all its pages removed from main memory to leave more room for ones that are active. Also, if the system is so overloaded that it is thrashing, swapping entire proccesses out may be the appropriate response.