[Mashiro]

I do believe Windows got its start on Xenix which was a Unix Flavor. They have since moved away from that, but it was a brief blip in Window's history. There was a split in the late-70's early-80s where Apple took parts of the BSD Core to create Darwin which is the foundation for macOS and Windows moved from Xenix to DOS when they started to finalize the build for Windows 1.

Microsoft licensed the rights to use the Xenix Unix flavor brand with their modifications under the name "Microsoft Xenix" from AT&T. Nothing to do with Windows though. It was/is a Unix version that Microsoft used to distribute.

> https://en.wikipedia.org/wiki/Xenix