What is Virtual Memory When you run a program on your computer, you use physical memory (RAM) to run it. You tell the computer to run the program and the processor pulls it from the hard drive and loads it into RAM so it can be worked with. You can only open so many programs until all of your RAM is being used. In order to open another program, you'd have to close one of the ones you have open in order to free up some space in RAM. Not with virtual memory!
Virtual memory is a technique utilized by your operating system in which it takes a chunk of your hard drive and uses it as memory. The programs you are running don't know the difference between physical memory and virtual memory, so it doesn't really matter that you run out of RAM, so long as you have some hard drive space as a backup for workspace. Essentially, you can choose to allocate as much free disk space as you have to be used for virtual memory. However, a hard drive is much, much slower than physical memory; therefore, it's not as reliable a place to run applications as physical memory, but it's a cost effective way to increase your workload without purchasing additional RAM.
If your virtual memory isn't configured appropriately to match your workload, you may receive an error from Windows saying that you have too little virtual memory or that your virtual memory is too low. This is often accompanied by a blue screen or can result in all of your programs being closed down and all of your work lost.