Game Development Dictionary
Virtual memory is a space in secondary memory (usually the hard drive) used to extend the "apparent" size of main memory (RAM). When all the RAM is currently in use, and more is needed, non-imperitve, low-priority, and/or suspended processes are paged out to virtual memory. Their process information is written to the harddisk, and the process image is deleted from the main memory, allowing a new process to begin. Low levels of main memory on high power systems require almost the constant use of virtual memory, which can lead to thrashing.