Virtual memory is a memory management technique used by an operating system (OS) to temporarily transfer data from random access memory (RAM) to disk storage, compensating for physical memory shortages. It is a storage allocation scheme in which secondary memory can be addressed as though it were part of the main memory. Virtual memory uses both hardware and software to map memory addresses used by a program, called virtual addresses, into physical addresses in computer memory. All memory references within a process are logical addresses that are dynamically translated into physical addresses at run time. Virtual memory works by dividing the virtual address space used by a program into smaller units called pages, and the operating system manages a mapping between virtual addresses used by the program and physical addresses in the actual RAM or disk. When a program accesses a virtual address that is not currently in physical memory, a page fault occurs, and the operating system retrieves the required page from disk and brings it into RAM, evicting other pages if necessary.

Benefits of virtual memory include increased memory capacity, memory isolation, and simplified memory management. Virtual memory is important for improving system performance, multitasking, and using large programs. However, users should not overly rely on virtual memory since it is considerably slower than RAM, and if the OS has to swap data between virtual memory and RAM too often, the computer will begin to slow down, which is called thrashing. Virtual memory was developed at a time when physical memory was expensive, and computers had a finite amount of RAM, so memory would eventually run out when multiple programs run at the same time. Virtual memory is an integral part of modern computer architecture, and implementations usually require hardware support, typically in the form of a memory management unit built into the CPU.