History of Mach

The Mach kernel began its life at the Carnegie Mellon University (CMU) [1] and was originally based off an operating system named ``Accent''. It was initially built inside the 4.2BSD kernel. As each of the Mach components were written, the equivilant BSD component was removed and replaced. Because of this fact, early versions of Mach were monolithic kernels, similar to xnu, with BSD code and Mach combined.

Mach was predominantly designed around the need for multi-processor support. It was also designed as a Micro-kernel, however xnu, the implementation used by Mac OS X, is not a micro-kernel. This is due to the fact that the BSD code, as well as other subsystems, are included in the kernel.