An Operating System is the basic software which manages a computer system. It handles how your hardware operates, the communication with peripherals for instance a monitor, a printer or a keyboard, the allocation of memory between all the applications, plus the prioritization of applications when several run at once. Each program that is installed on a desktop or a laptop functions by sending requests to the OS for different services by using an application program interface (API). The communication with the OS is possible using a Graphical User Interface (GUI) or a command line. In the Internet hosting field, the OS is what commands a web server and all the software installed on it, which includes not only website scripts, but also every other application for example a VOIP or a game server. If there're virtual machines created, they employ a guest OS which is run on the server host OS.