Paging File

(by Allan, at TweakXP.com)
The Paging File, or Swap File as it used to be known, is virtual memory . It's where the system will go when ram needs to be accessed but there is just no more room in your random access memory. It is a portion of the Hard Disk that is set aside as "virtual memory" (not really memory, but the computer is tricked into treating it as such). It's called a swap file because programs or files or .dll's or drivers will be swapped in and out as necessary by the Operating System. If you do not have a Paging File and you do run low on memory, everything will run much more slowly.