Virtual memory is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory (RAM) to disk storage.
Eventually, the OS will need to retrieve the data that was moved to temporarily to disk storage -- but remember, the only reason the OS moved pages of data from RAM to disk storage to begin with was because it was running out of RAM. To solve the problem, the operating system will need to move other pages to hard disk so it has room to bring back the pages it needs right away from temporary disk storage. This process is known as paging or swapping and the temporary storage space on the hard disk is called a pagefile or a swap file.
