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