The Cray Files

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Happy anniversary!

It was almost to the day 6 years ago that I started this project. It also happens to be 40 years ago that the first Cray-1 was shipped to the Los Alamos National Lab. So, to celebrate the anniversary I’ve pushed to release the 1.0 version of the simulator. Go to the download page to grab a copy and try it for yourself (and maybe have some cake too)!


These pages contain my project notes on how to build a Cray supercomputer at home. It was – and is – a fascinating journey to me into the history of computers. I’m writing my story up in hopes that others (well, you, dear reader) will find it interesting. It is somewhat of a living document, a journal of sorts. Though the story starts several years ago – and that part I recount from memory – I intend to add new pages to the files as I progress. When I tell this story I leave out some of the dead-ends and my wanderings in the digital desert, so the story-line feels more linear than it actually was. I don’t think you want to hear about all the dozens of failed attempts at solving something. I’ll only leave some of the most spectacular failures in for entertainment value.

  1. Prelude
  2. A New Hope
  3. The Hunt for the Red Bootcode
  4. The Return of the Cray
  5. The Matrix
  6. First update
  7. Needle in the Hay-stack
  8. A Brave New World
  9. Multiple Platforms
  10. Jobs
  11. Parallels
  12. Turbo

You can download the latest version of the simulator from the download page.

Special thanks to Andy Gelme, Scott G. Taylor, Brian Taylor and Chris Fenton without whom I would not have been able to get this project off the ground!

The picture above shows Cray X-MP serial number 302 being assembled after delivery. I got this picture from Andy who was the source of the OS backup disk that I’ve used for this project. It is the machine that I’m simulating! The following picture shows how it arrived to the lab: through a hole in the wall.


Help wanted!

Now that the Cray simulator is finally booting the OS, I have to plead for your help! I need SW to run on this. I need source code, I need compilers, I need tools. Without these, the machine is almost as dead as if I haven’t done anything. The OS is just the framework to do useful work in, but useless in itself.

If you have or know of anybody who has experience, old backup tapes, disks, anything that can be used with this machine, please contact me!

44 thoughts on “The Cray Files

  1. Pingback: » Cray-zy progress! We have a booting system!

  2. Pingback: Cray-zy progress! We have boot! » NYC Resistor

  3. You have your timeline a little wrong, I think. The Cray X-MP 2/2 was released before the Cray-2. I ran on a X-MP 4/8 at NASA/Ames for quite a while before they got their first Cray-2.

    • That could be the case, thanks for the input. I’ve seen conflicting information on the web about the release dates of these machines. I’ve tried to reconcile them to the best of my ability, but I could got things wrong. I certainly don’t have any personal memories from those days.

    • Great suggestion, thank you very much! I will contact them – let’s hope they still have some backups.

      • The e-mail you sent to ETH was forwarded to me, which lead me to your site.

        I worked for Cray Research in Zurich, where I was in charge of applications support and optimization. The X-MP of ETH Zurich was already decommissioned when I started working there in ’98, it was on display at the entrance of the computer center for many years. It was replaced with four J90’s, which were later replaced with two SV1’s. These machines were all running UNICOS, not COS. As far as I know the only thing left from this era is the X-MP chassis (which is no longer functional since many components were removed before it was put on display), and a few programming & optimization manuals that I kept as a souvenir.

        The Cray Museum in Chippewa Falls used to have a nice collection of CDC and Cray systems. Maybe someone there can help you — if this museum still exists.

        Good luck!

  4. You might try contacting While they don’t list the system your working with. They are restoring some systems to active status and never know they might have some old software in their archives. Worth a shot.

    • Thanks for the suggestion. I’ve been in contact with the Cray-Cyber folks and they don’t have anything X-MP related. The Y-MP EL they have is a substantially different architecture, and last time I’ve checked even that was down.

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  6. You might try contacting the National Museum of Computing. They recently restored a Cray Y-MP EL to working condition: The 12/02/2011 update mentions that they created backup copies of all the disks (8×3 GB data, 200 MB system). That might be interesting to get a copy of; it surely has compilers installed (see the second screenshot). The museum has a significant archive of software and disks, as described at the end of this newsletter: The museum’s contact email is

  7. Hello Andras,

    maybe a stupid question: is there the assembler in the disk pack ? I suppose so.
    So we could also use some source listing, and compile a compiler from the scratch.

    Then, another question, is there a way to create a tape or another medium in order to run a job ? Putting in another way, how can I write and run a job using the simulator ?


    • Unfortunately there isn’t any assembler on it either. I’ve found one dataset, that contains the following utilities:

      • AUDIT
      • TEDI
      • PLD10
      • GENCAT
      • ACCTDEF
      • JCSDEF
      • PRVDEF
      • LOADCAT
      • RECALL
      • RELOAD
      • RECIO
      • DMP10

      That’s all I have.
      There are two ways of transferring files into the simulator. The best probably is to put files on the expander disk, by recreating it. You can use the build_exp_disk.bat file as a template to do that.
      The other way is to rename the file(s) you want to put on the tape to 1.dat, 2.dat, etc. and move them into the ‘boot_tape’ folder. Than they should be accessible from the expander tape.

      The final question is: how to create a job file. It seems to me that these files would need to be part of a dataset, where each line is a separate record. The dataset format is documented in here for example: I have written a tool (dataset_extractor) that can crack a dataset open and extract the individual files and records from it, but I didn’t do the reverse: to assemble a dataset from individual files. That’s on the TODO list.

  8. One thing that struck me when comparing to Chris Fenton’s older site is that you made little mention of xmpsim.

    xmpsim was a Cray simulator / XMP CAL interpreter for x86 MS-DOS PCs, written by Kay A. Robbins and by Steven Robbins of the University of Texas at San Antonio. Version 1.01 was the last known version, apparently dating from March 12, 1988.

    It has some nice features, such as the ability to produce a Gantt chart showing pipeline timing.

    xmpsim is described in the book entitled “The Cray X-MP/Model 24 : A Case Study in Pipelined Architecture and Vector Processing”.

    You can also find some information on how to use the simulator in Japanese here:

    or an English tutorial here:

    Even some lecture notes!


    Chris Fenton has xmpsim available for download here:

    I don’t know if you want to contact Steven Robbins or not, don’t know if he can help you and/or Chris at all…

    • Thanks for the comment. I was aware of XMPSIM, I probably should have mentioned it. The difference between what Steven did there and I did is that while his is a fairly accurate simulation of the CPU pipeline, mine is a much less accurate simulation of the whole system – I/O, peripherals, interrupts. I’ve contacted Steven in the past but he was unable to help unfortunately.

      Thanks again,

  9. Marvelous effort!
    I am presently restoring a 1972. HP2000 TSB system, real hardware :), and hope to have it running on the internet probably this year.
    Anyway, my major interest in computing was always in a way “parallel processing”, so a Cray is very interesting!
    Why I write to You here (except to congratulate You on what You did) is to mention that I found this Lady on LinkedIn:

    On another note, isn’t it absolutely weird how we succeeded to forget all we did in the 80-ies and early 90-ies. All the software lost… Recovering discs from magnetic image scans… We must be a strang civilisation… It is only 20 to 30 years!!!

    Wish you all the best!!!

    BTW: Regarding software development, there is always the “full bootstrap” possibility. Having a specification of the internal workings it is always possible to write a cross-assembler, then to write the assembler in Cray assembly language, transfer it to the simulator, and start up something like described by William Waite in “Implementing Software for Non-numeric Applications”, what he calls STAGE-2, a macro language capable for (cryptic) writing of compilers. I used this approach back in the mid-80ies to boot up an operating system and Pascal compiler for a industrial control multi-micro-computer system I designed using MC6809 processor(s).
    And there is always the GNU … for Cray …

  10. Hello,
    thank you very much for your hard work, its very important to preserve this fantastic machine!

    have you tried to contact ?

    Or Mr Robert “Bo” Ewald, he worked in Los Alamos when they had 5 Cray….

    please don’t give up!!!!

    Thanks again

    • Thanks! I have talked to the Computer History Museum, they don’t have anything that they can help with. I’ll try to track down Robert. So far Los Alamos could not help with anything either (and they were using CTSS, not COS). Having more leads could never hurt though, so thanks again.


  11. Have you considered contacting the people at

    They seem dedicated to enthusiasts being able to see how these machines worked. On their terms of usage page it says:
    “These machines are originally intended to preserve the old culture and machines and make them available for everyone who just wants to play around, do software developing or whatever.
    Everyone is welcome, have a great time and do not hestitate to contact us if you have questions. ”

    I bet they would help in any way they can. 🙂

  12. We helped port Unix to the Cray (Bell Labs). I did some command porting. Dennis Ritchie was the lead of this project.

    • This is great, nice to meet you! I assume this was not UNICOS, right? Which machine did you use for the port?


  13. Our system became Unicos on the Cray X-MP. We wrote the C compiler also. I’m checking to see if there’s any trace left of the compiler work.

  14. I met Chris Fenton at a NY Maker Faire a couple of years ago, but I just learned about your work. We loved working on the Cray (I really worked on the Cray – I used to sleep on the circular bench when I had to spend all night fixing disk failures)

  15. The late Dennis Ritchie’s home page has moved. The current URL is
    and the article “Experiences with the Cray X/MP” is at:

    As for, there hasn’t been much activity there in quite a while. As of 2014-03-04, their machines had to be shut down. They were planning to move them, and were hoping to be back some time in 2014 (unfortunately that didn’t happen). There have been no posts on the diary since then.

  16. What happened to cray-1x repo in They are now empty. I searched for cray-1x on GitHub but all clone repos are empty too. There were no repos on sourceforge. Thanks.

    • Unfortunately Google changed their servers around and won’t support (maybe it does now, but didn’t for a while) SubVersion. As a result we’ve moved the repository to a private server. I periodically do source releases on the website though and of course if you wish to contribute I would be more than welcome to give you access.

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