virtual memory

A computer will have a limited amount of real memory available to it. Programs often require more memory than the amount of real memory. Furthermore, in a multiprogramming system, different processes will be competing for the same limited supply of real memory. An operating system overcomes these conflicts by allocating an amount of virtual memory to each process, which might be larger than the total amount of real memory. This is possible by storing unused parts of a process's address space on disk, until such time as it is required. When required, it is swapped in to part of the real memory, whose previous contents are swapped out to disk.

In computer systems, the memory as it appears to, i.e., as it is available to, the operating programs running in the central processing unit (CPU). Note: The virtual memory may be smaller, equal to, or larger than the real memory present in the system.