Microsoft Windows is a series of graphical interface operating systems developed, marketed, and sold by Microsoft.
Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs).<ref name=aboutcomnov>Template:Cite web</ref> Microsoft Windows came to dominate the world's personal computer market, overtaking Mac OS, which had been introduced in 1984.
The most recent client version of Windows is Windows 7; the most recent server version is Windows Server 2008 R2; the most recent mobile version is Windows Phone 7.5.The most recent unstable release is Windows 8.