Windows 4.0 was the original planned name for the product code-named Chicago, which was eventually released as Windows 95.
The first-ever version of Windows NT was called version 3.1. The public reason that it was called 3.1 is is to keep it parity with the then current version of 16-bit Windows which was at that time Windows version 3.1.
Industry rumour at the time was that the real reason it was called Version 3.1 was that Microsoft had a contract in place with Novell which gave them some confidential internal details of how the Novell NetWare IPX/SPX network protocol and the NetWare network client worked.
At the time that NT was in beta, Novell still did not have a client for the new operating system. Microsoft had to write its own client so that the new NT operating system would be able to connect to Novell NetWare servers over Novell's own network protocol. So the first several versions of Windows NT what bundle with a Microsoft written Novell network client, and subsequently a third-party client became available from Novell itself which implemented additional functionality such as support for the Novell NDS directory system.
The licensing agreement between Microsoft and Novell only covered up to and including Windows version 3.1. Therefore in order to use that information, that was the version number that Microsoft had to use for the new product.
I also add to that that you include another red herring that Microsoft's marketing department put out in your comment. The Windows 9X and Windows NT product lines were never merged.
Windows 2000 internally was Windows NT version 5.0. It changed to using plug and play device enumeration so that it could boot on p&p systems designed for Windows 9X. It was able to cope with not knowing the IRQ or DMA channels in use for its boot hard disk for example.
So what that means is that Windows 2000 was the version that incorporated support for the key technology that enabled Windows 9X but which could prevent NT 4 from running effectively on such machines.
Windows 2000 was meant to be the first consumer-focused version of the Windows NT product family... But Microsoft got cold feet, was afraid that it wasn't quite ready, and pushed out one more iteration of the 9X product line: Windows ME. Then it gave a bit of cosmetic facelift to Windows NT 5, added theming to the GUI, substantially increased the speed of boot up and suspend and resume, called it Windows NT 5.1, the marketing department branded it as "Windows XP", and the rest is history. But it doesn't actually include any technology from Windows 9X.
As I understand it some people from the DOS-based Windows product development team were moved over to the Windows NT development team, and the rest were laid off. Not many people were transferred and no technology whatsoever -- there never was a merger.
I don't think that qualifying XP as merely 2000 with a facelift is not entirely fair. XP benefited from having drivers produced for 2000 by the time it came out, but it also had additional compatibility shims to allow almost every Windows application in existence to work (in 32bits). 2000 was a great OS, that I liked, but it wasn't ready for consumers (not dissimilar to the Vista/7 situation). I believe that waiting until XP for the NT kernel big push was the right one, even if it gave us Me which was likely the worst release of the OS.
Windows 4.0 was the original planned name for the product code-named Chicago, which was eventually released as Windows 95.
The first-ever version of Windows NT was called version 3.1. The public reason that it was called 3.1 is is to keep it parity with the then current version of 16-bit Windows which was at that time Windows version 3.1.
Industry rumour at the time was that the real reason it was called Version 3.1 was that Microsoft had a contract in place with Novell which gave them some confidential internal details of how the Novell NetWare IPX/SPX network protocol and the NetWare network client worked.
At the time that NT was in beta, Novell still did not have a client for the new operating system. Microsoft had to write its own client so that the new NT operating system would be able to connect to Novell NetWare servers over Novell's own network protocol. So the first several versions of Windows NT what bundle with a Microsoft written Novell network client, and subsequently a third-party client became available from Novell itself which implemented additional functionality such as support for the Novell NDS directory system.
The licensing agreement between Microsoft and Novell only covered up to and including Windows version 3.1. Therefore in order to use that information, that was the version number that Microsoft had to use for the new product.
I also add to that that you include another red herring that Microsoft's marketing department put out in your comment. The Windows 9X and Windows NT product lines were never merged.
Windows 2000 internally was Windows NT version 5.0. It changed to using plug and play device enumeration so that it could boot on p&p systems designed for Windows 9X. It was able to cope with not knowing the IRQ or DMA channels in use for its boot hard disk for example.
So what that means is that Windows 2000 was the version that incorporated support for the key technology that enabled Windows 9X but which could prevent NT 4 from running effectively on such machines.
Windows 2000 was meant to be the first consumer-focused version of the Windows NT product family... But Microsoft got cold feet, was afraid that it wasn't quite ready, and pushed out one more iteration of the 9X product line: Windows ME. Then it gave a bit of cosmetic facelift to Windows NT 5, added theming to the GUI, substantially increased the speed of boot up and suspend and resume, called it Windows NT 5.1, the marketing department branded it as "Windows XP", and the rest is history. But it doesn't actually include any technology from Windows 9X.
As I understand it some people from the DOS-based Windows product development team were moved over to the Windows NT development team, and the rest were laid off. Not many people were transferred and no technology whatsoever -- there never was a merger.