When inspecting the Environment System Variables I noticed that the Environment Variable "OS" is set to "Windows_NT".

To my knowledge the Windows NT operating system was released in the 90s and has long been deprecated. I would have expected it show something along the line of "Windows_10".

The PC is also brand new so I didn't change the Environment Variable to show "Windows_NT", so I am fairly certain that it does so by default on Windows 10.

So why does Windows 10 list "Windows_NT" under the Environment Variable "OS"?

  • 6
    Windows NT is still used all over the place in the registry and folder/file names. Sep 26 at 13:27
  • 15
    Windows NT was the name of the first Windows version that had the "new architecture" (compared to Windows 9x). The core of Windows NT is used since then in Windows 2000, XP, Vista, 7, 8, 10, 11...
    – Robert
    Sep 26 at 13:27
  • 4
    Windows 2000+ are all based on the NT kernel. with the only exception being Windows ME, Windows RT and Windows on ARM are modified versions of the NT kernel that support ARM.
    – Ramhound
    Sep 26 at 14:36
  • 3
    And NTFS is still the filesystem.
    – Davidw
    Sep 27 at 4:36
  • 11
    @Robert: "Compared to 9x" is a bit misleading. NT predates even Windows 95. NT was the 32 bits alternative to Windows 3.x; the Windows 9x series was a kludge mixing Win16 and Win32.
    – MSalters
    Sep 27 at 8:18

2 Answers 2


Even though "NT" is no longer part of the marketing names, all current Windows versions still use the exact same NT system architecture (which is distinctly different from Windows 95/98/ME). Internally, Windows 2000 calls itself "NT 5.0" as it is a direct descendant of Windows NT 4, while the Vista-Win10 series is "NT 6.x".

In a somewhat similar way, macOS calls itself "Darwin", Solaris and Illumos call themselves "SunOS", and some projects still group current Linux kernel versions under "linux26" (as the 2.6.x series brought in major changes from 2.4, while later restarts in numbering such as 3.x have no such significance).

  • 5
    Wikipedia gives a list of marketing versions and their corresponding NT versions.
    – Jason C
    Sep 27 at 0:29
  • 3
    @OrangeDog WIndows NT was only the "marketing name" for NT up to version 4. Later the name "NT" was used for the kernel/architecture. Since Windows 2000 (and let's not forget the Windows CE and RT versions) "Windows NT" has effectively become Microsoft's equivalent to Apple's Darwin. IIRC Darwin was actually a (short-lived) OS on its own, designed as successor to NextStep. Apple bought it all and kept Darwin as kernel but redesigned the OS to create MacOS.
    – Tonny
    Sep 27 at 9:21
  • 4
    Then I guess a better comparison would have been NeXTSTEP to macOS, as many macOS APIs are still named after "NSThisOrThat"...
    – user1686
    Sep 27 at 9:34
  • 3
    While Windows 7 = NT 6.1, Windows 8 = NT 6.2, and Windows 8.1 = NT 6.3, Windows 10 actually does report its internal version number as NT 10.0.
    – user46971
    Sep 27 at 16:34
  • 6
    @user46971 That's true ... but Windows 11 also reports version 10.0, not even version 10.1!
    – IMSoP
    Sep 27 at 19:07

In the 1990s, Microsoft had two largely independent OSes, both branded as "Windows":

  • The original "Microsoft Windows", which was a graphical shell on top of MS-DOS
  • A completely new operating system, which originated in a collaboration with IBM on OS/2, and was internally code named "NT", based on the hardware they were testing with.

The first version of the new OS was marketed as "Windows NT 3.1", to imply that it was similar to the existing "Windows 3.1", even though it was essentially a different product - they could just as easily have called it "Microsoft NTOS 1.0". The main thing the two "Windows" products shared was the "look and feel", although there was some support for running the same programs on both OSes.

The two products then continued in parallel for a while: the DOS-based OS (with large parts of MS-DOS itself replaced) had releases named "Windows 95", "Windows 98", and "Windows Me"; while the NT-based OS had releases named "Windows NT 4.0" and "Windows 2000". The two products continued to share a "look and feel", and a few components, but still had fundamentally different internal architectures.

At this point, Microsoft abandoned the DOS-based product, and continued only the NT-based one. This is the OS that is still branded as "Windows" today: "Windows XP", "Windows Vista", "Windows 7", "Windows 8", "Windows 10", and "Windows 11" are all continuations of that project.

Since they've never "thrown it away and started again" since the original "Windows NT 3.1", those OSes are still internally labelled "Windows NT" in various places.

  • 3
    Windows 95 and newer isn't "a graphical shell on top of MS-DOS". What was the role of MS-DOS in Windows 95?
    – Syroot
    Sep 29 at 15:06
  • 1
    @Ray I never exactly said it was, but I've clarified a bit. Note the last paragraph of that article, which confirms that large parts of MS-DOS were in fact still used. Possibly you could say there were three Windows OSes: DOS-based, 9x, and NT-based; but I think that would just complicate the story.
    – IMSoP
    Sep 29 at 15:29

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