Windows NT 3.x NT 3.1 Pre-Release
Windows NT 3.1 was the first of the Windows NT series. Sporting the same face as its consumer counterpart Windows 3.1, it was completely different under the hood. A true 32-bit native operating system, Windows NT descended from the work Microsoft did while collaborating with IBM on OS/2 after the great split, and bringing in former DEC employees like Dave Cutler, bringing a VMS influence into the system. It was followed up by Windows NT 4.0.
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Release notes
These builds are early pre-releases, that lead up to the final NT 3.1. They are ocasionally referred to as "NT OS/2", as the core technology was developed by Microsoft for use in future IBM OS/2 products. However, after the IBM-MS split, it became "Windows", and is branded as such.
The very first builds are visibly little more than the Win16 API and Windows 3.x GUI ported to a 32-bit system.
Microsoft Windows NT 3.1 (10-16-1991) October 1991(ISO)
Microsoft Windows NT 3.1 (3.10.196) (9-16-1991) SDK (ISO)
Microsoft Windows NT 3.1 (3.10.340) (10-12-1992) (3.5-1.44mb)