Microsoft Windows is a series of popular proprietary operating environments and operating systems created by Microsoft for use on personal computers and servers. Microsoft first introduced an operating environment named Windows in 1985, as an add-on to MS-DOS. This was in response to Apple Computer's then-new computer system, the Apple Macintosh, which used a graphical user interface (GUI). Microsoft Windows eventually came to dominate the world personal computer market with market analysts like IDC estimating that Windows has around 90% of the client operating system market. All recent versions of Windows are fully-fledged operating systems.