An Operating System is the software which communicates with the hardware of a computer and functions as the intermediary between applications and the hardware, which includes peripheral devices such as a printer, a computer mouse or a keyboard. When you run an app, it transfers requests to the OS using an API (Application Program Interface) and the communication is done through a command line or a Graphical User Interface (GUI). Identical to a personal computer, hosting servers also use an Operating System which acts as a host for all of the software installed on them, including script apps or server-side software such as a flash server, a VOIP server, and many others. A virtual machine can be created on a physical one, so it is possible to install a guest OS on it and have a different system environment compared to the physical server host Operating System.