Virtualization is the process in which you can simulate for example an operating system inside a machine that is currently running another operating system. Basically, the operating system is using a virtual hard disk drive (VHD, VDI) instead of using the physical partition of your drive and it runs using virtual emulated devices such as (keyboard, mouse, graphics, CPU, etc). Virtualization is available for hardware, desktop, network, software, memory, storage, data and network. Almost any of these devices and system are possible to emulate under a virtual operating system.