[JPLeRouzic]

As written in the article, Xenix was a Version 7 UNIX, so it was not written by Microsoft and as ATT didn't licensed the name 'UNIX', Microsoft had to use another name.

I have fond memories of the much more recent Windows 2000, it was a relief from the horrors of Windows ME. Contrary to UNIXes which ran on black box hardware (DEC/SUN/Apollo, etc) Windows ran on PCs where everyone could write a driver, and it (more or less) works with the OS.

Microsoft offered an interface for drivers and tools to validate them:

https://en.wikipedia.org/wiki/Windows_Driver_Model

[rbanffy]

2000 was fine. A nice upgrade for NT 4, but Unix has been running on PCs for a long time, and writing a device driver, while not trivial, was a very well documented process. The fact that, besides PCs it ran on high-performance exotic hardware made scaling up the easy choice before scaling out came into fashion.

As it not being written by Microsoft, that's one thing that makes it the last good operating system Microsoft has ever sold - someone who knew what they were doing wrote it for them ;-)