An Operating System is the basic software which controls a computer. It handles how your hardware behaves, the communication with peripheral devices for instance a monitor, a printer or a keyboard, the allocation of memory between various applications, and the prioritization of apps in case several run simultaneously. Every program that is installed on a desktop or a notebook works by sending requests to the OS for different services using an application program interface (API). The communication with the OS can be achieved using a Graphical User Interface (GUI) or a command line. In the Internet hosting field, the OS is what runs a web hosting server as well as all the software installed on it, which includes not only website scripts, but also any other application for instance a VOIP or a game server. In case there are virtual machines created, they employ a guest OS that is run on the server host OS.