What Is The Virtual Memory And Its Function?

An imaginary memory area supported by some operating systems (for example, Windows but not DOS) in conjunction with the hardware. You can think of virtual memory as an alternate set of memory addresses. Programs use these virtual  addresses  rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses are converted into real memory addresses.  The purpose of virtual memory is to enlarge the address space, the set of addresses a program can utilize. For example, virtual memory might contain twice as many addresses as main memory. A program using all of virtual memory, therefore, would not be able to fit in main memory all at once. Nevertheless, the computer could execute such a program by copying into main memory those portions of the program needed at any given point during execution.  To facilitate copying virtual memory into real memory, the operating system divides virtual memory into pages, each of which contains a fixed number of addresses. Each  page  is stored on a disk
until it is needed. When the page is needed, the operating system
copies it from disk to main memory, translating the virtual addresses
into real addresses.  The process of translating virtual addresses into real addresses is called mapping. The copying of virtual pages from disk to main memory is known as paging or swapping.

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A virtual memory is known as a computer system technique which is used as Systems using virtual memory technique along the RAM works more efficiently rather than the ones that works without this technique.

Virtual memory is a computer system technique which gives an impression to an application program as like it has an adjacent working memory. On the other hand it might be a possibility that an overflow on the disk storage or physical fragmentation may exists. Now a days almost all computer OS use this technique as like for normal applications that include spreadsheets, word processors, players etc. In simpler terms this virtual memory is used as to extend the memory but not by overlapping or swapping data.

Some Operating System say Windows(XP,Vista, 7) enables a process to use a memory (RAM) address space that is not dependent of other processes running in the same system,
and use a space that is larger than the actual amount of RAM present,
temporarily relegating some contents from RAM to a disk, with little or no overhead is the Virtual Memory.