Getting Nostalgic With the Historical Coherent Operating System

The 90s was a wonderful decade. Apart from great music, you also had interesting tech. Coherent was part of the 90s UNIX-like operating systems.

Here’s a blast from the past. Years ago, back in the early 1990s, there was an operating system called Coherent. The price wasn’t so bad – $99. A few years ago, it was made freely available. Coherent never claimed to be UNIX, but UNIX-like. I learned a lot with that OS.

When the Mark Williams Company closed in 1995, Coherent was a closed-source product. In 2015, it was released under a 3-clause BSD License so, if you’re interested, you can grab a free copy of Coherent at Internet Archive or here.

Here’s a little look-back at Coherent.

Coherent’s Requirements

Coherent was able to run on most Intel-based PCs with Intel 8088, 286, 386, and 486 processors. Coherent version 3, the version I started on, required at least a 286, and Coherent version 4 needed a 386. The drives that were supported were MFM or RLL.

coherent v3.0 ad 1
coherent v3.0 ad

Coherent 3.0 which was a clone of the AT&T V7 UNIX. It ran very well on a ‘386 and 20mb MFM drive. When Coherent 4.0 came out, I upgraded and also replaced the hard disk to a 40mb MFM unit. In both cases, Coherent ran on less than 10mb. Coherent 4 was closer to AT&T’s Sys5R4 UNIX.

Coherent 3.0 was a 16-bit OS but Coherent 4.0 was a bigger upgrade, able to take advantage of 32-bit operations. It still had a handful of programs limited to 16-bit operations, but all in all, it was a good system.

Coherent’s Offerings

For a small package, it was remarkably complete. Not only was it a standalone operating system, but came with a big box of goodies, such as a Bourne Shell, C compiler, assembler, debugger, DOS disk support, uucp, at least three editors, some games, mail, and around 200 of the most used and useful UNIX commands.

coherent v4.0 ad2
coherent v4.0 ad

The shell had a few bugs and was missing some features, but it was sufficient for the small stuff I normally did with it. X Windows was available, but I don’t think it came with the basic system and, if I remember correctly, was a separate purchase. I remember having it and it worked, but it had a few problems, but the Mark Williams Company continually worked on it.

Using Coherent

Having a small UNIX system on a personal PC at home was nice. I was well versed with DOS, but UNIX was the operating system in use where I worked at the time and I preferred it over DOS and Windows 3.1. Coherent wasn’t as powerful as UNIX but it was a good learning tool. With it, I learned much about system administration and got a massive amount of hands-on experience with the command line.

Programming was fun, but since the C compiler only had small model support (64K of code and 64K of data), I was limited in what programs I could write. Some might laugh at the small model, but some nifty programs could be written with it.

Using Coherent at home, I was a single user, using it mainly for the experience with the command line and to learn a bit about system administration.

I really can’t recall how well Coherent handled networking; I never concerned myself with it. I don’t recall it having a lot of network support – it certainly didn’t have TCP/IP. However, it did have uucp. It took me some time to get it working right, but once that was done, it delivered all the Usenet news I could ever want.

One might think that it wouldn’t do well in a large setting, such as a school, but I attended one college that actually had several Coherent workstations. They were used mainly as training stations for classes in operating systems.

The XWindows vs. TCP/IP Argument

There are some arguments over whether or not the Mark Williams Company’s efforts on XWindows was wise, or if they should have concentrated on implementing a TCP/IP stack. To some, this is the main reason why the Mark Williams Company folded.

The Mark Williams Company spent a lot of time and effort on getting X Windows to work. I don’t recall that they truly finished, but they had at least gone a long way toward completing it. It makes sense to me that they would focus on it – the goal was to make an affordable UNIX-like system and X was definitely considered a part of UNIX.

A small company would have to choose its projects carefully. XWindows was chosen. Even Linux, in its early days, didn’t offer TCP/IP support at first – KA9Q was used for a short time, so I don’t think that the decision to focus on XWindows was unwise at all.


Coherent just couldn’t keep up with the competition and the Mark Williams Company closed in 1995. I certainly don’t consider Coherent a failure in the slightest, however. It was an excellent UNIX option at the time and the efforts of the Mark Williams Company was quite impressive.

I learned more about the command line and general system administration than I ever could have where I worked at the time. I once recommended Coherent to an individual who wanted to learn UNIX on her own. After a year with it, she hired on as a system administrator. The last I heard from her, she was the senior UNIX admin at a large site in the Midwest US.

I’m right glad that I got to play with Coherent. I credit Coherent with being a key part in my education; it had a part in how my career developed and I went on to be a system administrator on different UNIX systems.

At home, I would eventually settle on Linux – a decision I do not regret, but if you decide to play with it remember that it’s old – you will be experiencing a bit of history. If you would like to try out Coherent, you can run it through VirtualBox. Thorough setup instructions can be found at: Not only does the page cover VirtualBox setup, but the page also contains a link to disk images and installation instructions – a one-stop site.

About the author
Bill Dyer

Bill Dyer

Bill has worked in the computer field as a technician, programmer, and UNIX system administrator. He is currently a continually caffeinated programmer/analyst who spends some spare time building e-bo

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