Microsoft Windows is a series of 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 of personal computer markets 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. Windows is mostly closed source software: Microsoft Corporation owns the software's copyright and controls its distribution.
Windows was developed for IBM PC-compatible computers, and today, almost all versions of Windows are made for this hardware-platform (although Windows NT was written as a cross-platform system for Intel and MIPS processors, and later appeared on the PowerPC and DEC Alpha architectures). The popularity of Windows made Intel CPUs more popular and vice versa. In fact, the term Wintel became used to describe PC-compatible computers running a version of Windows.