Virtual Memory is really just part of the hard drive that is reserved for the operating system to do what is called "paging". Data is stored in memory in "pages", and only a certain number of these can fit in physical memory (RAM) at any given time. Therefore, the operating system takes some of these pages and moves them out to virtual memory, so that the more current pages (usually the ones for the program being used at the moment) can be kept in physical memory, which is faster. This process is often referred to as "swapping", hence the term "swap file". The swap file is essentially nothing more than one huge file that contains often thousands of these pages on a reserved portion of the hard drive.

Virtual Memory Settings
The default paging file size is 2 MB. The recommended paging file size for Windows 2000 is equal to 1.5 times the total amount of RAM. Windows will set a default paging file size during installation. In some circumstances, such as when a large number of applications are running simultaneously, using a larger paging file or multiple paging files might be beneficial. Unused space in the paging file remains available to the internal Windows Virtual Memory Manager.

If Windows detects that the Windows Paging file is set too low then an error message will appear after logging on, stating "Virtual Memory Minimum Too Low". The message indicates that Windows is increasing the size of the paging file. While this occurs, any programs that are running may run more slowly or they may pause because any memory requests by those applications may be denied.

SWAP File Errors
In some instances SWAP file errors or "Swap file Corrupt" messages may display, indicating that the permanent swap file that was created for Windows has become corrupt. The most common reason that swap file errors are received is if the amount of hard drive space is running out. This error may also appear when disk management functions like FORMAT and FDISK are running. Sometimes the Swap file can be overwritten or become corrupt.