Windows 8.1 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 1, 2012, and later to retail on October 26, 2012. Windows 8 is the first version of Windows to support the ARM architecture, under the Windows RT branding.
See also: Windows 8.1, Windows Phone 8, Microsoft Windows, Windows 10, Windows 8 editions, Windows To Go.