http://windows.microsoft.com/en-US/windows-vista/What-is-virtual-memory http://windows.microsoft.com/en-US/windows-vista/Change-the-size-of-virtual-memory Virtual memory, also known as a page file or swap file, is a file on your hard drive (C:\pagefile.sys by default) that Windows and applications use in addition to physical memory (RAM) as needed. The default and recommended size of this file is 1.5 times the amount of physical memory. Virtual memory is the sum of physical memory and the page file. So if your computer has 512 MB RAM, it will have a 768 MB page file by default, for a total of 1.25 GB of physical + virtual memory.
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What is virtual memory?
If your computer lacks the random access memory (RAM) needed to run a program or operation, Windows uses virtual memory to compensate.
Virtual memory combines your computer’s RAM with temporary space on your hard disk. When RAM runs low, virtual memory moves data from RAM to a space called a paging file. Moving data to and from the paging file frees up RAM to complete its work.
The more RAM your computer has, the faster your programs will generally run. If a lack of RAM is slowing your computer, you might be tempted to increase virtual memory to compensate. However, your computer can read data from RAM much more quickly than from a hard disk, so adding RAM is a better solution.
Virtual memory and error messages
If you receive error messages that warn of low virtual memory, you need to either add more RAM or increase the size of your paging file so that you can run the programs on your computer. Windows usually manages the size automatically, but you can manually change the size of virtual memory if the default size is not enough for your needs. If you receive warnings that your virtual memory is low, you'll need to increase the minimum size