Virtual Memory is a mechanism by which applications function as though the system has more RAM than it actually does. Virtual memory operates by paging unneeded code to a file on the hard drive called the swap file or page file.
In Microsoft Windows 2000 and Windows NT, the Virtual Memory Manager maps the virtual addresses belonging to the address space of a running process to physical pages of memory in the computer.
This ensures that each process has sufficient virtual memory to run efficiently and does not trespass on the memory of other processes. The Virtual Memory Manager handles paging between RAM and the page file, swapping pages by using a process called demand paging.
The result is that each application has access to up to 4 GB of memory. A similar process in Microsoft Windows 95 and Windows 98 uses a comparable structure called the swap file.
In Microsoft Windows 2000, you can use the System Properties property page to change the maximum size of the page file.