It is actually more complicated than that. https://en.wikipedia.org/wiki/MacOS_version_history https://en.wikipedia.org/wiki/MacOS_version_history https://en.

It is actually more complicated than that. https://en.wikipedia.org/wiki/MacOS_version_history https://en.wikipedia.org/wiki/MacOS_version_history https://en.wikipedia.org/wiki/MacOS_version_history#/media/File:Unix_history-simple.svg https://en.wikipedia.org/wiki/MacOS_version_history#/media/F... There is a "base" of MACH/NextStep that is partially based on "original" BSD and then there are some parts added later coming from both FreeBSD and NetBSD.