An Operating System is the software which communicates with the hardware of a computer system and functions as the intermediary between applications and the hardware, which includes peripheral devices such as a printer, a mouse or a keyboard. When you run an application, it transmits requests to the OS using 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 use an Operating System which serves as a host for the software installed on them, which includes script apps or server-side software such as a flash server, a VOIP server, and many others. A virtual machine can be generated on a physical one, so you will be able to install a guest OS on it and have a different system environment compared to the physical server host Operating System.