Windows NT

The term Windows NT was used to distinguish Microsoft's line of business-orientated operating systems from their consumer-orientated versions. The numbering system effectively started from Windows for Workgroups 3.1, with the first Windows NT release being Windows NT 3.1. Windows NT 3.5, Windows NT 3.51 and Windows NT 4.0 would be the only other operating system releases to bear the Windows NT branding (although the beta for Windows 2000 began as Windows NT 5.0).

This is a summary of where Microsoft products ended up on the Windows NT versioning system: