Coherent was a Unix clone for IBM compatibles Mark Williams Company produced and sold in the 1980s and early 1990s.

What environment and tools was Coherent developed with? Was it cross-developed on another Unix system?

2 Answers 2


I emailed this question to Steve Ness, who worked at Mark Williams Company from 1977 through 1995 on Coherent and other projects. This is his answer, which I share with permission:

Mark Williams Co. used a PDP-11 as development platform before COHERENT came up, once COHERENT booted all development shifted quickly to COHERENT-based.


MWC never had any Unix machine in-house. Some of the developers had previously used Unix at Waterloo.

Many thanks to Steve Ness for the information.


According to this article and a few others around the net, Coherent was originally written on and for the DEC PDP -11. It was then ported to other processors, including x86.

  • Thanks for the link. The article says Coherent was originally developed for the PDP-11, but leaves out whether it was developed on the PDP-11. Are there sources confirming the latter? Commented Jan 16, 2022 at 11:58
  • 1
    Based on groups.google.com/g/alt.folklore.computers/c/_ZaYeY46eb4/m/…, an argument could be made that development started on a PDP-7 as AT&T Unix, but I am hesitant to say that with any more certainty than Dennis Ritchie had. Commented Jan 17, 2022 at 23:23
  • Having said that, I'd be surprised if Mark Williams Co had anything other than a PDP-11 to do development on. Commented Jan 18, 2022 at 0:01

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