For what it's worth, the entire list of released (not alpha, not beta, not Release Candidate, not (in one case) a beta add-on to a release version, although a couple of these are a bit iffy as far as not being beta - namely, Premiere Edition 1.00, and ) Windows versions by major and minor version, as far as I know. I'll note that, with NT 3.10, and with Windows 4.00, Microsoft began transitioning to doing fairly major functionality changes and bug fixes in service packs or OEM Service Releases, whereas before they did them in minor version changes. I'll list those in parentheses.
1.0xWindows Premiere Edition 1.00
Windows 1.01 (added Write)
Windows 1.02
Windows 1.03
Windows 1.04
2.0xWindows/386 2.01
Windows 2.02 (might have just been the 8088 build?)
Windows 2.03 (also available as Windows/286 and /386)
2.1xWindows 2.10 (only available as /286 or /386)
Windows 2.11 (only available as /286 or /386)
3.0xWindows 3.00
Windows 3.00a
3.1xWindows 3.10 (also available as Windows for Workgroups, which added SMB/NetBIOS/NetBEUI support)
Windows 3.11 (also available as WfWG, which added an updated kernel with 32-bit driver support and the aforementioned SMB/NetBIOS/NetBEUI support)
NT 3.10Windows NT 3.10 (RTM build 511, RTM build 528 (apparently added DEC Alpha support), SP1, SP2, SP3 - I might have this slightly wrong)
NT 3.5xWindows NT 3.50 (RTM, SP1, SP2, SP3)
Windows NT 3.51 (added PowerPC support and some bugfixes, RTM, SP1, SP2, SP3, SP4, SP5)
4.00Windows 95 (RTM, SP1/OSR1, OSR2, USB Supplement to OSR2, OSR2.1 (slightly updated kernel from the USB Supplement), OSR2.5)
NT 4.00Windows NT 4.0 (RTM, SP1, SP2, SP3, SP4, SP5, SP6, SP6a)
4.10Windows 98 (98, 98 Second Edition)
4.90Windows Me
NT 5.00Windows 2000 (5.00 - RTM, SP1, SP2, SP3, SP4)
NT 5.01 - I'll note that during this time, Microsoft started changing how they displayed their version numbering. Most versions of NT 5.01 display their version as 5.1.
Windows Advanced Server Limited Edition (ASLE 1.0 (and this one identified as both Windows Whistler (XP's codename) and as Windows 2000
), ASLE 1.1 (not sure if this displays as 5.01 or 5.1, or what it IDs as))
Windows XP (displayed as 5.1 - RTM, SP1, SP2, SP3 - also in a "64-Bit Edition" (RTM, SP1) for Itanium)
Windows Datacenter Server Limited Edition (don't know how it displayed)
NT 5.02 (displayed as 5.2)
Windows Advanced Server Limited Edition 1.2
Windows Server 2003 (RTM, SP1, SP2)
Windows XP 64-Bit Edition, Version 2003 (RTM, SP1)
Windows Server 2003 R2 (RTM (2003 SP1 with added features), SP2)
Windows XP x64 Edition (RTM (based on 2003 SP1), SP2)
NT 6.00 (displayed as 6.0)
Windows Vista (RTM, SP1, SP2)
Windows Server 2008 (RTM, SP1, SP2)
NT 6.01 (displayed as 6.1)
Windows 7 (RTM, SP1)
Windows Server 2008 R2 (RTM, SP1)
NT 6.02 (displayed as 6.2)
Windows 8 (RTM)
Windows Server 2012 (RTM)
I'd say it's fair to lump any .0x change in minor version before NT 5 together (I've seen more functionality added by a service pack, than by any .0x change before NT 5.01), so that means there's 1.0x, 2.0x, 2.1x, 3.0x, 3.1x, NT 3.1x, NT 3.5x, 4.00, NT 4.00, 4.10, 4.90, NT 5.00, NT 5.01, NT 5.02, NT 6.00, NT 6.01 (being the 16th version by that measurement), and NT 6.02.
Now, given that Windows 7 is consumer oriented, let's remove every NT prior except for 5.01 and 6.00, and forget about 6.02 (because it's just incrementing by one)... now it's 1.0x, 2.0x, 2.1x, 3.0x, 3.1x, 4.00, 4.10, 4.90, 5.01, 6.00, 6.01, or eleven versions.
Combine 2.0x and 2.1x, the changes were really quite minor as I understand (much less than some service packs *cough*XP SP2, 2003 SP1*cough*), we're to ten. Combine 3.0x and 3.1x, even though the changes were much more major there (and 3.11 had an edition with very major changes), we're to nine. Combine 4.00, 4.10, and 4.90 (I can actually make the case for combining 4.00 and 4.10, there's more difference between 98 and 98SE, than there is between 95 OSR2.5 and 98, but 4.90 is actually quite different under the hood), we're finally to seven.