An Operating System is the software which communicates with the hardware of a computer and works as the intermediary between the installed applications and the hardware, including peripheral devices such as a printer, a mouse or a keyboard. When you run software, it transmits requests to the OS using an API (Application Program Interface) and the contact 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 the software installed on them, which includes script applications 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 in contrast with the physical server host OS.