Windows 8.1 is a version of Windows and the second and last version of Windows 8.x. It was released on October 17, 2013, the same date as Windows Server 2012 R2. It is part of Windows NT 6.x, Windows 8.x, and one of the Windows 201x versions. It is the successor to Windows 8, and the predecessor to Windows 10. It is also a free update of the operating systems Windows 7 (under certain conditions) and Windows 8.