Virtual Memory

At times the computer uses all the RAM (Random Access Memory) so in this case the system has to use part of the hard disk space as if it were RAM. This space is what is called Virtual Memory. In windows you can change its size by changing the size of the Paging File >>>

1. OPEN computer management
   
2. In the console tree, right-click Computer Management (Local), and then select Properties.
3. On the Advanced tab, click Performance Options, and under virtual memory, click Change.
4. In the Drive list, click the drive that contains the paging file you want to change.
5. Under Paging file size for selected drive, type a new paging file size in megabytes in the Initial Size (MB) or Maximum Size (MB) box, and then click Set.

   If you decrease the size of either the minimum or maximum page file settings, you must restart your computer to see the effects of those changes. Increases generally do not require a restart.

In Linux there is a special Partition called the SWAP Partition. It's the same thing