Coherent: The affordable Unix-like PC OS from over a decade before Linux 0.01

> Anyone that used it or wrote code for it hated it.

I didn't! Used Coherent 3.0.0 and all later versions and wrote quite a few programs for it and ported many more. UUCP packages, news readers, wrote my own CU clone, my own mail client, etc. It was a real Unix system for $99 and fit easily on a 20MB ST-225 hard disk with plenty of space for your own stuff. I loved Coherent.

Maybe in commercial software development things look different, but for me as a hobbyist it was a dream coming true.

[Submitter here]

> I am curious to the attraction of Coherent now.

TBH I am not sure that it has one.

> Anyone that used it or wrote code for it hated it.

{{citation needed}}

I knew a few owners. They loved it. Until Linux, Coherent was the cheapest way to get a UNIX OS on a PC.

> It was not compatible with any version of Unix.

That is not fair or reasonable or accurate for the time.

This was a 1980s product. No 1980s Unix was compatible with any other. That's why the iBCS existed:

https://en.wikipedia.org/wiki/Intel_Binary_Compatibility_Sta...

They were all different, even though all were based on some version of the same AT&T kernel or code derived from it.

Coherent was so close and so compatible that AT&T believed it must have been based on stolen code and sent Dennis Ritchie himself to visit the company and check.

Here are his comments from that visit:

https://groups.google.com/g/alt.folklore.computers/c/_ZaYeY4...

«

An anecdote: sometime fairly early after the Mark Williams company started offering their Coherent system (a Unix clone), some AT&T legal people asked me to visit Mark Williams for purposes of determining whether what they were offering was a rip-off (i.e. essentially a copy) of the currently licensed Unix done by us. I find it hard to reconstruct the date this happened, but it was a long time ago; probably early 1980s. I went to Chicago with Otis Wilson, who was then involved in Unix licensing.

It was a rather strange experience. The Mark Williams company was a paint producer, and I was given to understand that the subsidiary that was doing Coherent was, approximately, a corporation arranged by a father who, approaching retirement, had more or less shut down the older business and was using the corporate name and legal setup to help his son in a new venture.

Otis and I visited the offices of Mark Williams on the outskirts of Chicago and were received with courtesy and some deference. We talked to the father and the son (Bob Swartz, i.e. the guy behind Coherent). There had been communication before, and from their point of view we were like the IRS auditors coming in. From my point of view, I felt the same, except that playing that role was a new, and not particularly welcome, experience. The locale of the company was in an industrial section and it definitely retained the flavor of a the offices of a paint company being recycled.

What I actually did was to play around with Coherent and look for peculiarities, bugs, etc. that I knew about in the Unix distributions of the time. Whatever legal stuff had been talked about in the letters between MWC and AT&T didn't allow us to look at their source. I'd made some notes about things to look for.

I concluded two things:

First, that it was very hard to believe that Coherent and its basic applications were not created without considerable study of the OS code and details of its applications.

Second, that looking at various corners convinced me that I couldn't find anything that was copied. It might have been that some parts were written with our source nearby, but at least the effort had been made to rewrite. If it came to it, I could never honestly testify that my opinion was that what they generated was irreproducible from the manual.

I wrote up a detailed description of this. I can't find it, probably because at the time I was advised that it was privileged lawyer/client material. Partly at the time, partly thereafter, I learned that a variety of Unix enthusiasts (several from U. Toronto) had spent time there.

In the event, "we" (=AT&T) backed off, possibly after other thinking and investigation that I'd wasn't involved in.

So far as I know, after that MWC and Coherent were free to offer their system and allow it to succeed or fail in the market.

I suppose there's a second story about the suit by USL against BSDI and then UCB, but my own involvement was far tinier and didn't get me a trip to Falls Church or Berkeley to snoop. What advice I offered in this situation was exactly in line with that about MWC/Coherent, and as it turned out the resolution (though more costly for all) was pretty much the same.

(As a capper, Bob Swartz came by Bell Labs a week or so ago, and we had a pleasant social visit.)

Dennis

»

You just had to have been there. Sure Interactive made a better Unix than Coherent, but it required a 386. MINIX wasn't out quite yet. Apple's Unix required an expensive Mac. 68k based workstations were expensive. I ran Coherent on a 286 I inherited.

In this era people were accustomed to platforms offering slightly different Dev tools and capabilities. When you wanted an apple ii program to run on a c64, you had to PORT it. There was no java. There was no gcc. The STL was neither S, nor exclusively T or L. C compilers were often proprietary, written by companies making hardware. And had different takes on the language. The reason that C89 is called C89 is the standard was ratified in 1989, almost a decade after coherent was first released.

In '89, paying $500 for Interactive/386 made sense. But in '85, you couldn't do that, so $100 for coherent on a 286 or even 8086 was a decent alternative.

For someone who didn't earn much it was a godsend. It looked and felt enough like real UNIX that I was happy to buy it for home use.

However work was all Xenix/UNIX/AIX/Ultrix/etc.

I didn't know the company was founded by Robert Swartz. I'd always see the magazine ads for Mark Williams C, and just ssumed that it was written by a programmer named Mark Williams who made a company.

Another fun fact: One of the Coherent's authors was Tom Duff (of Duff's Device fame) apparently.

I went to a technical highschool with focus on informatic, so for our operating systems class the introduction to UNIX was done via Xenix.

It was a PC tower, that the teacher would rent from his work once a week.

Given the timeframe, we would split in groups, having prepared our samples as best as we could in Turbo C for MS-DOS, with dummy implementations for the UNIX calls not available on MS-DOS.

Then we would take 15m turns, to try to make our applications run in Xenix with the actual real implementations, instead of the stubs.

Current generations have no idea how expensive it was to get into computers.

The classic "Nautilus" manual was really interesting on two sides; one was the quality of the writing, which was all down to Fred Butzen - he just had a real knack for clarity and working with him on documenting the work I did during the 4.0 process was really enjoyable. Basically the process was that developers would write up drafts of everything to give to him, and he'd then edit them for clarity before passing them back for an iteration to ensure that none of the accuracy was lost. He just had an excellent sense of when there was going to be a better explanation than the classic dry manpage style.

The other notable thing about that manual was just the economics of getting a perfect-bound book of that sheer size printed and included in the USD99 price tag.

The documentation was incredible! I ran Coherent when I was in high school and that's how I learned "Unix" and C programming, before moving to Linux.

FWIW, if Coherent did no fold, I would have stuck with it.

Yep, I recall it being $99, but I thought mine came with a perfect-bind paperback book, probably with a nautilus shell on the cover. I bought it, but there was some showstopper for my needs, maybe that it only supported 64KB processes(?), so I returned it.

Today, our pocketbooks are spoiled by open source, few-dollar phone apps, and you're-the-product SaaSes. $99 (in decades-ago dollars) was often a bargain price for a lot of nontrivial PC software. That was also the price of Borland Sprint (cheaper than Wordperfect), and Borland Turbo Assembler&Debugger 1.0 bundle (Microsoft's assembler costs hundreds), both of which I bought while grossing $3.65/hr. As a teen, I briefly sold a simple program-launching menu program for MS-DOS for $24.95 (and about broke even, after packaging costs).

There was also Minix. I used to have a binder with the source code, eons ago.

I don't know about the current state of Coherent support, but the Wikipedia page has some resource links.

https://en.wikipedia.org/wiki/Coherent_%28operating_system%2...

Coherent was published by Mark-Williams, who also had their own C compiler (MWC), which was also available for CP/M86 and the Atari ST. It's a K&R compiler, so expect some trouble with compiling modern code (unprotoize might help a bit here).

The final releases of Coherent (4.2 is the last one IIRC) also fully supported the iBCS COFF binary standard, so binaries compiled for e.g. SCO Unix might work.

You could also try to build an old gcc version with the provided K&R compiler: https://www.autometer.de/unix4fun/coherent/coh_prog.html

Copies of BSD have been traded at various prices since the 70s ranging from "free, but bring your own tapes" at user groups to a few hundred bucks (about a couple thousand dollars today) for a packaged distribution with documentation. However BSD was tangled up in a lawsuit from 1991-1994, right as Linux was launched online as a free download.

You'd likely find the experience pretty miserable, not so much because of the C compiler - Steve did a great job with that - but actually because of the filesystem. Coherent was around for a long time, remember; it used a very classic V6 UNIX filesystem, complete with odd endianness of 32-bit fields in the inode and most significantly, the classic 14-character file name length.

That right there will be an even bigger showstopper for the build scripts of most things than anything else. During the early 90's we could run GCC and Comeau C++ and all that kind of thing on Coherent fine because those codebases were still built for wide portability even though things like BSD FFS had opened that up - there were still plenty of machines running System III and System V code that most people took care not to create gratuitous collisions if truncation happened. Even shortly post the advent of Linux, that had changed dramatically and basically turned on its head and the effort involved in backporting to any flavour of classic UNIX (not just Coherent) quickly became almost impossible.

Coherent had a K&R C compiler, so modern software would simply not compile. There is a tool called "unproto" that compiles ANSI (C89) programs with K&R compilers, and there is a Coherent version on my homepage (http://localhost/t3x.org/index.html#retro -- scoll down a bit). However, even this will probably not get you ver far with modern software.

For 32-bit Coherent (4.0.0 and later) there is some 2.x GCC, but I have never used it and I doubt that it can compile software that is "modern" these days.

> I had no idea there was a unix-like available at relatively reasonable cost before Linux.

That is why I posted the link.

Linux was not the first low-cost Unix for the PC.

Very roughly, it went:

* Unix only ran on proprietary kit. PCs were too small.

* The 286 came along, and SCO took over Microsoft Xenix and offered it as a 286 OS -- expensive, and stuff we take for granted now, like networking, X11, and a compiler, were all separate expensive extras.

* The 386 made Xenix a very credible usable OS, but it cost 10x as much as DOS or Windows. Commercial deployments in business, with no GUI, no networking, no compile, just statically-linked proprietary apps and dumb RS-232 terminals, mostly from Wyse.

* As PCs got more powerful, other companies offered expensive PC Unixes too, and SCO officially licensed the AT&T kernel: SCO Xenix became SCO Unix.

* Coherent came along with a very cheap and complete (but very limited) Unix-like OS.

* Minix came along, even cheaper and you could get the source code.

* It became possible to build and run BSD on PCs if you were a serious guru.

* GNU considered the BSD kernel and decided against it, going for Mach and the HURD instead. (Oops.)

* Linux came along and undercut Coherent, putting the MWC out of business.

* NetBSD and FreeBSD became somewhat usable if you were highly capable.

* Linux gradually became somewhat usable as a mainstream OS, with things like live CDs (Yggdrasil, Lasermoon Linux-FT) and installable modular distros with packaging (Red Hat Linux, Debian).

It's not based on V6, although it was basically created as a clone of it (and on the PDP-11, no less - the x86 versions of Coherent until 4.x were basically just minimal ports that kept the PDP-11's classic 16-bit flavour). It was a very very good clone, enough that a lawsuit was threatened and Dennis Ritchie himself got pulled into checking that it wasn't derived from any UNIX source - see dmr's comment at https://groups.google.com/g/alt.folklore.computers/c/_ZaYeY4...

Cool! I had my hands on it, too. For some reason it got traction in late USSR.

You were fortunate to have one of the few computers it would actually run on.

Probably because somebody had the tarballs lying around, somebody else said "dude, that's so cool, you need to put them on github", and the first person grudgingly obliged. Seems reasonable to me to defer the labor of unpacking and organizing everything to the person who thinks it's really cool, instead of the person who regrets not cleaning out their desk sooner.