> MacOS because XNU is based on Mach, and it was forked (Edit: from 4.3BSD) in 1988 As another commenter noted: XNU = Mach + FreeBSD. What you are referring t

> MacOS because XNU is based on Mach, and it was forked (Edit: from 4.3BSD) in 1988 As another commenter noted: XNU = Mach + FreeBSD. What you are referring to is what NeXTSTEP was, Mach + BSD4: * https://en.wikipedia.org/wiki/NeXTSTEP#Unix https://en.wikipedia.org/wiki/NeXTSTEP#Unix By the time Apple got to them it was a few years later, and so they decided to updated that part of the kernel, and also brought in FreeBSD's userland.