Microsoft Windows is a succession of graphical interface operating systems developed, marketed, and sold by Microsoft Corporation. The company introduced an operating environment named Windows as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs), on November 20, 1985. The most recent client version of Windows is Windows 7; the most recent server version is Windows Server 2012; the most recent mobile version is Windows Phone 7.5. An operating system (OS) is a compilation of software that manages computer hardware resources and gives common services for computer programs. It is a very significant component of the system software in a computer system. Application programs need an operating system to function. It can be sorted out by technology, licensing, ownership, working state, usage, and by many other characteristics, and it can be found on almost any device that contains a computer, from cellular phones and video game consoles to supercomputers and Web servers.