Virtual memory

A system that stores portions of an address space that are not being actively used in some medium other than main high-speed memory, such as a disk or a slower auxiliary memory medium. When a reference is made to a value not presently in main memory, the virtual memory manager must swap some values in main memory for the values required. Virtual memory is used by almost all uniprocessors and multiprocessors, but is not available on some array processors and multicomputers, which still employ real memory storage only on each node.