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Mach (1986) booting on a SIMH VAX
Type: Multitasking, multiuser
Creator: CMU
Architecture: VAX, m68k, m88k, i386, i860, ROMP, POWER, HPPA, Sparc
This Version: 3.0 (1994)
Date Released: 1985

Mach was the microkernel from CMU that popularized the microkernel craze of the late 1980's and into the 1990's. While seen as a dead end effort, it did at the time bring in many new things to the aging Unix kernel. Mach, based loosely on BSD was a low level kernel adding threads insteads of forked processes, and had the ability to run on SMP hardware. BSD was then ported back as a user process on top of the Mach micro kernel.

Archived Releases

I'm putting together a list of all the versions of Mach that I have tracked down over the years. I'll add in building & running instructions as I can. If you know or are in possession of other releases, please let me know!



During the original development started at CMU, using various accent technologies and 4.3BSD as a starting point. There is 2 partial trees for these releases made in 1986. I'm assuming these are some version 1.x thing Both of these releases are on Kirk's DVD set.


There is currently 2 versions saved of the '2.5' variation, both were found on the CSRG CD-ROM set.

  • mk35
  • X147


Starting with 3.0 the 4.3BSD kernel was removed from the source making this a 'pure' Microkernel. So far the following versions have been saved:

  • mk42
  • mk78
  • mk80
  • mk82
  • mk83
  • mk83a
  • mk84


After the winding down on Mach research at CMU, the University of Utah picked up Mach in 1994 and was released as Mach4. Known releases are:

  • UK02p21
  • UK22

Further work went into the OSKit, a modular system to build kernels.

Later on Mach4 was shut down, and later attention was put into the new L4 kernel.


The OS/F group made various releases based on the Utah versions. Many were encumbered, however I have managed to track back a few releases:

Mach Operating Systems

Some of the operating systems that used Mach were NeXTSTEP/OPENSTEP, Mach386 & OSF/1. The GNU Hurd project also used Mach at one point before abandoning it for L4.

The GNU project had taken a version of Mach, and used the GNU license to 'gnu-ify' mach and produce GNUMach. While Windows NT may share design ideas with Mach, it is NOT a derived Mach microkernel.


Mach could run various 'server' programs that would then provide an operating system personality to the user.


4.4 BSD subsystem. It was pulled at the start of the lawsuit


BSD Net/2 subsystem


One of the more popular servers was Lites. It was a BSD based personality that could then run early versions of NetBSD & FreeBSD.

There was also a msdos subsystem


Mach was seen as unnecesary as its main idea of running multiple servers hardly ever happened. Most projects based on Mach only ran a single server. Also every time a program made a system call it had to transition through the kernel to talk to the 'server' process, which had to go thru Mach again to do whatever it was, then back to the server, then thru Mach again to talk to the program. The overhead of the system call was was significant, and a way was never developed to bring the LPC calls down to something comparable to an older monolithic style OS. This is why XNU (the Nextstep/Openstep/Darwin/OSX kernel) used Mach as a library rather then as a full blown microkernel.

The rise of Linux also showed that a re-structured monolithic kernel could not only scale on SMP hardware, but could remain portable.

Getting it to run

Installing Mach on the PC is not a task for the timid. It is VERY involved and difficult. I have decided to provide an image here. I may document the install later, but it is extremly complex.