An Operating System is the software that communicates with the hardware of a PC and serves as the intermediary between the installed applications and the hardware, which includes peripherals such as a printer, a computer mouse or a keyboard. When you run software, it transfers requests to the OS through an API (Application Program Interface) and the interaction is done via a command line or a Graphical User Interface (GUI). Identical to a personal computer, hosting servers also feature an Operating System which functions as a host for all the software installed on them, which includes script applications or server-side software such as a flash server, a VOIP server, and so on. A virtual machine can be set up on a physical one, so it is possible to install a guest OS on it and have a different system environment in contrast with the physical server host OS.