[TickleSteve]

Mach was never based on BSD, it replaced it. Mach is the descendant of the Accent and Aleph kernels. BSD came into the frame for the userland tools.

"Mach was developed as a replacement for the kernel in the BSD version of Unix," (https://en.wikipedia.org/wiki/Mach_(kernel))

Interestingly, MkLinux was the same type of project but for Linux instead of BSD (i.e. Linux userland with Mach kernel).

[laurencerowe]

It's not just the user land but much of the BSD kernel too. From https://en.wikipedia.org/wiki/Mach_(kernel)

> Throughout this time the promise of a "true" microkernel had not yet been delivered. These early Mach versions included the majority of 4.3BSD in the kernel, a system known as a POE Server, resulting in a kernel that was actually larger than the UNIX it was based on.

And https://en.wikipedia.org/wiki/XNU

> XNU was originally developed by NeXT for the NeXTSTEP operating system. It was a hybrid kernel derived from version 2.5 of the Mach kernel developed at Carnegie Mellon University, which incorporated the bulk of the 4.3BSD kernel modified to run atop Mach primitives,

MkLinux is similar. https://en.wikipedia.org/wiki/MkLinux

> The name refers to the Linux kernel being adapted to run as a server hosted on the Mach microkernel, version 3.0.