Also, what are VM's used for?
They operate almost exactly, but not quite, as another complete hardware box. I can have 4 different PC's, with 4 different operating systems running all at once, on one physical box. You save on hardware, power, heat.
WinXP, Linux, and Server 2012 all running at the same time. The host system, in my case, is Windows 8 Pro.
Testing, software development, a myriad of uses. Also, they can easily be rolled back to a previous state.