Memory overcommitment occurs when applications allocate and commit more memory than is actually available in the computer. OS/2 handles memory overcommitment by copying memory to the system swap file, SWAPPER.DAT, on the hard disk then reusing the memory for another allocation. OS/2 copies as many pages of memory as are necessary to make room for the new allocation. The swapped memory can be retrieved the next time it is accessed; at that time, some other memory might be written to the swap file.
OS/2 selects the memory to swap based on when it was last used. The page that is least-recently-used, that is, the page that has gone the longest since its last access, is the page chosen to swap to disk.
Swapping is transparent to an application, although excessive swapping can cause an application to run slowly.
Through swapping, OS/2 enables applications to allocate more memory than actually exists in the computer, bounded only by the amount of free space on the hard disk that contains the swap file.