Virtual computer memory allows desktop and laptop systems to locate empty random access memory (RAM) required loading other programs or working faster in the utilities that are open.

How It Works
Virtual memory creates your computer believe it has more memory than it does by copying an unwanted portion of RAM onto the hard drive.

Amount of Virtual Memory
In Windows OS, virtual memory is 1.5 times the physical RAM, according to Microsoft. Divide it between different hard drives can make the most of virtual memory.

Adjustments
Virtual memory is also called the paging file. If your OS is something other than Windows XP, you can check both "Virtual memory" and "Paging file" in the "Help" section of your OS manual.

Low Virtual Memory
Your computer alerts you when your virtual memory is running low. This typically means that you are running lots of programs or other program which use large amount of memory.

Thrashing
When your HDD is being overworked because it is sending information between RAM and virtual memory, according to Computerhope.com. Thrashing can cause a computer to run very slow and cause a HDD to burn out rapidly.