Virtual Memory

Virtual memory is a memory management technique that lets a computer run programs needing more memory than the physical RAM installed. The operating system gives every program its own large, private address space and moves blocks of memory, called pages, between RAM and a reserved area of the disk as they are needed.

The disk area is called the page file on Windows and swap space on Linux. Virtual memory also isolates programs from each other, so one program cannot read or corrupt another's memory. Because disks are much slower than RAM, heavy use of virtual memory (thrashing) makes a computer noticeably slow.