What is "virtual memory"

n. (context computing English) Memory that appears to be RAM but is being simulated (by a process called paging) on a hard disk; allows a computer to operate as if it had more memory than it actually does, but with some loss of performance

n. (computer science) memory created by using the hard disk to simulate additional random-access memory; the addressable storage space available to the user of a computer system in which virtual addresses are mapped into real addresses [syn: virtual storage]

In computing, virtual memory is a memory management technique that is implemented using both hardware and software. It maps memory addresses used by a program, called virtual addresses, into physical addresses in computer memory. Main storage as seen by a process or task appears as a contiguous address space or collection of contiguous segments. The operating system manages virtual address spaces and the assignment of real memory to virtual memory. Address translation hardware in the CPU, often referred to as a memory management unit or MMU, automatically translates virtual addresses to physical addresses. Software within the operating system may extend these capabilities to provide a virtual address space that can exceed the capacity of real memory and thus reference more memory than is physically present in the computer.

The primary benefits of virtual memory include freeing applications from having to manage a shared memory space, increased security due to memory isolation, and being able to conceptually use more memory than might be physically available, using the technique of paging.