Your computer uses virtual memory to extend the amount of available RAM by writing physical memory (RAM) to disks through a process called paging. With paging, Windows 7 writes a set amount of RAM, such as 1,834 MB, to the disk as a paging file, where the operating system can access it from the disk when needed in place of physical memory.
Windows 7 writes paging files to disk drives as a file named pagefile.sys. Windows 7 creates an initial paging file automatically for the drive containing the operating system. By default, other drives don’t have paging files, so you must create these paging files manually if you want to use them. However, in most instances, you won’t need to put a paging file on multiple disks, as doing so won’t necessarily boost performance. As with many other aspects of performance, Windows 7 does a much better job than its predecessors do of automatically managing virtual memory. Typically, Windows 7 will allocate virtual memory at least as large as he total physical memory installed on the computer. This helps to ensure that paging files don’t become fragmented, which can result in poor system performance.
You can also manually manage virtual memory. If you do this, you’ll typically want to use a fixed virtual memory size. You fix the size of the virtual memory by setting the initial size and the maximum size to the same value, and this in turn prevents fragmentation of the paging file.