An Operating System is the software that interacts with the hardware of a PC and works as the intermediary between all the applications and the hardware, including peripherals 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). Similar to a personal computer, hosting servers also have an Operating System which serves as a host for the software installed on them, including 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 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.