Commodore 900: The Unix-like workstation/server that was eclipsed by Amiga

Some time ago I acquired a Commodore 900 computer.  It was originally owned by one of the engineers who worked on the project but it needed some attention to get it to work.

The Commodore 900 had a a few internal names judging by the documentation including early references to the

Commodore 900 hi-res workstation configuration

“S8000”, the “Z800” and the “M-Series Z8001” but it were a lot of references to “Z8000HR” because it was based on the Zilog Z8000 architecture and there was both a multi-user server option and a Hi-Resolution workstation option. The C900 (short for Commodore 900) ran an early version of Coherent 0.7.3 that was a Unix work-alike OS by the Mark Williams Company.  It ran a customized version for the C900.  The documentation I have for this computer is available at the following location:  There you can find lots of internal documents and schematics along with the Coherent manuals.

The example C900 I have can be configured in two ways:

  1. With the monochrome display card, the C900 can be configured as  a low-resolution server that can utilize a monochrome monitor for text-only output. This would be sufficient enough for mange the C900 as a multi-user server.
  2. With the HR display card, the C900 can be a high resolution graphics workstation.  This card includes a 9 pin connector for a custom Commodore mouse.  The High-resolution monitor known as the “HR monitor” (no model number yet) is a 1024×800 pixel paper-white display that was quite impressive for 1984/1985.

Clearly the market for the C900 was the Unix workstation/server market for education and research that would spill into the business side one the upcoming networking was to be put into place.  Unfortunately, it didn’t make it that far.

Commodore was in the process of acquiring Amiga and focus was turned away from the C900 and the potential that was there.  It was a departure from what Commodore was known for and was already a market leader in the home computer segment.  It was a little more familiar than the education and research markets that Commodore had a small role in with the PET.  But that was a dwindling market for them.

The C900 could have been a competitive product along side Sun and HP workstations in 1985 but the direction changed and the C900 project was cancelled.  Some say it never worked properly but I was able to get my C900 up and running.

Often compared to the design of the Amiga 2000, the C900 was designed earlier and the styling were used on the Amiga 2000.  There are some differences in dimension even though some believe it is the same case.  You can see the difference in this image.

I still have some more exploring to do as I was able to get the C900 running for the first time on October 15, 2020.  Two power supplies later and some careful massaging of the 20MB Miniscribe 3425 hard drive that was stuck brought life back to this computer. My initial exploration was of the early version of Coherent.  I have experience with Unix but I do find it odd that all of the networking utilities are missing (they were not available yet). It would certainly make archiving attempts easier but I will have to rely on the custom quad-density 1.2MB floppy drive and likely the serial port that can do 19,200 bps at best.

During my initial exploration, I was able to find a Commodore 900 demo that was likely used in the Hannover Fair in Germany in 1985.  This video shows it running on my C900.  Further work is ongoing in trying to archive the hard drive contents and finding a more permanent workable hard drive solution.

Here is another demo called “csoup” or “chicken soup”.  It was among another demo called “chicken”.  It is the C900 drawing the Commodore logo onto a star field background.  I should have known that was what “chicken” was.

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6 Responses

  1. Sudos says:

    You should consider adding your images of your fully-working 900 to the Wikipedia article for this model. There doesn’t seem to be an image on the page of either a complete system nor the size difference to the Amiga 2000.

  2. Juan Fonseca says:

    Great review of an obscure hardware and even more rare Unix-like software for Commodore!

  3. roberto says:

    Is a pleasure to find this rare news and articles on the unknown c900. Thank you so much also for all the datas and specs provided

  4. Badscrew says:

    Wow, a 1024×800! Lovely.

  5. Jan Janssen says:

    I need help! I have a C900 Server and I have the Coherent installation disks but I am missing the disk to partition the drive. Has anybody this disk and is able to make me a copy? Or can anyone partition my harddisk in the C900 way (it is different to the PC way of partitioning the disk). I would love to see the machine finaly running.
    Thank you!
    BTW: I have a spare floppy drive and a spare server-board (the lores one).

    • admin says:

      Hi Jan,

      Please contact me directly via the “Contact Us” link on the top of the opening website page. I’ve been trying to contact you but it doesn’t seem that I’ve had any luck.

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