Virtual memory is the amount of hard drive space used by the system to suppliment the physical memory installed. In 2000, XP, and now Vista the page file is the end result of this. On older versions of Windows 9X-ME it was referred to as the swap files. The cache is onboard memory for hardwares like hard drives called disk caches pronounced as "cash" rather then ca che'. Or it is a portion of the physical memory installed reserved. Some good definitions are given in the online dictionary page seen at http://www.webopedia.com/TERM/c/cache.html