An Operating System is the low-level software which manages a computer. It handles how the hardware functions, the communication with peripheral devices for instance a monitor, a printer or a keyboard, the allocation of memory between applications, along with the prioritization of applications when several run concurrently. Any program which is installed on a laptop or a desktop functions by sending requests to the OS for various services by using an application program interface (API). The interaction with the OS is possible via a Graphical User Interface (GUI) or a command line. In the hosting field, the Operating System is what controls a hosting server along with any software installed on it, which includes not only website scripts, but also any other application for example a VOIP or a game server. In case there are virtual machines created, they employ a guest OS which is run on the server host OS.