Windows NT
Windows NT is the current line of Windows operating systems developed by Microsoft. This includes:
- Windows NT 3.1 through 4.0
- Windows 2000 (NT 5.0)
- Windows XP (NT 5.1 & 5.2)
- Windows Vista (NT 6.0)
- Windows 7 (NT 6.1)
- Windows 8 (the next version, planned for mid-2012)
...and most likely future versions of Windows as well.
Windows NT does not include Windows 3.x or Windows 9x/Me, none of which were actual operating systems, but rather graphical shells that ran on top of DOS.
For more information, including a more inclusive list of NT versions, see Wikipedia's Windows NT entry.