A virtual PC is effectively a software version of a physical PC which is able to run its own operating system and applications. Typically a virtual PC will boot up in its own window and is often used to run a different operating system to the one installed on the host pc on which it runs. You could therefore use it to try out a version of say, Linux, without having to install it on your main system.

Microsofts free Virtual PC software has been available to do this in versions of Windows up to and including Windows 7, but has been superseded in Windows 8 by the faster and more robust Hyper-V system which is incompatible with other virtualisation software.