An Operating System is the software that interacts with the hardware of a computer and serves as the intermediary between apps and the hardware, which includes peripherals such as a printer, a computer mouse or a keyboard. When you run an app, it transfers requests to the OS through an API (Application Program Interface) and the communication is done via a command line or a Graphical User Interface (GUI). Just like a personal computer, web hosting servers also have an Operating System that acts 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, and so on. 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 OS.
