Not only was it based on OS/2 it even supported some of the OS/2 APIs for awhile, along with things like the HPFS filesystem:

https://web.archive.org/web/20090210125723/http://www.micros...

https://support.microsoft.com/en-us/help/100108/overview-of-...

See https://en.wikipedia.org/wiki/OS/2#1990:_Breakup for more information about how they diverged over time.

The statement "NT is based on OS/2 3.x" is misleading. NT isn't based on OS/2 3.x, it was originally meant to be OS/2 3.x, until the IBM-Microsoft divorce. But, despite being originally intended to be OS/2 3.x, there was not much OS/2 1.x/2.x code in it. The main areas of inherited code were HPFS and the OS/2 compatibility subsystem, neither of which ended up being core features, and were dropped in newer releases. Outside of those, there was very minimal code inherited from 1.x/2.x. "NT is based on OS/2 3.x" makes it sound like NT inherited more of the design or implementation of OS/2 1.x/2.x than it actually did.

Allow me to enlighten you a little bit.

"The family link between OS/2 and Windows NT" https://liam-on-linux.livejournal.com/54138.html

"Follow-up: the family links between DOS, OS/2, NT and VMS" https://liam-on-linux.livejournal.com/54464.html

There's a citation in that 2nd blog post. Well, there are lots, but the IT Pro Mag one goes into detail about the OS/2 and VMS connection.

Enjoy.