Virtual memory is a method where each process is given its own address space (virtual memory), and the hardware translates every VM reference to a physical memory address. Originally VM was used to provide more address space than the available physical memory. To accommodate situations when more virtual memory is in use than physical memory, a storage device such as HDD can be used to "swap out" data and later "swap (back) in" as needed.
Virtual memory originally was used to provide more address space than the available physical memory. Nowadays virtual memory is employed so that each process can be given its own address space (virtual memory), and the hardware (the Memory Management Unit, MMU) translates every virtual memory reference to a physical memory address. To accommodate situations when more virtual memory is in use than actual physical memory, space on a storage device (the backing store, or swap space or page file) such as HDD, SSD or even thumb drive can be used to "swap out" data and later "swap (back) in" as needed. The swapped data is usually in data lengths called pages, but there are alternate schemes that use variable length segments or even paged segments.
