Mach was first described in a paper [#!machorig!#] to Usenix in 1985. It was developed at Carnegie Mellon University to form the base for their operating system research. It was initially based within 4.2BSD, replacing its components with Mach components as they were completed. When 4.3BSD was released, the remaining BSD components were updated. The first release of Mach, Release 0 took place in 1987. Several more releases followed until Release 3 in 1990, by which stage the BSD components had all been removed from the server to run as a single-server on top of the `bare' Mach microkernel. The University of Utah took over development of Mach in 1995 to form the basis of their research into operating systems and added new features.
They released Mach 4 in 1996. They have since continued in their research with a project called Fluke. GNU now distribute a version of Mach that is based upon the Mach4 release from Utah.
Mach has been used as the basis for commercial operating systems; Version 2.5 was used as the basis of the NeXTStep operating system and also the basis of OSF/1 Unix. The OSF still maintain a separate copy of Mach, now based on Mach Version 3. Recently, the OSF have ported Linux to run on top of their version of Mach.
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