Virtual memory is a technique to provide more address space than the available physical memory. Each process can be given its own 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.

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