A replica of the PDP-10 (KA10) mainframe computer

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32 bits is not enough, but 64 bits is just silly. The PDP-10 was DEC's fabulous exactly-right 36-bit mainframe (or superultramini, because - definitions). This was the machine that Gates & Allen used to write Basic for the 8080, before they had even touched a real 8080. It was where Hacker Culture grew, emacs was born, and where the debugger could be the CLI. User interface things only went downhill from there.

After the PDP-8 & -11, this will complete my DEC trilogy. It uses the same approach: inside is a Raspberry Pi with simh. Run TOPS-10, TOPS-20 (yes, but), ITS. Play spacewar on the GT340 display; log in over simulated Knight TV terminals, or over the internet thanks to the IMP interface. All work already done by a band of PDP-10 aficionados, I should add: this is just putting a physical form to it: a 36-bit laptop, 21 inches wide, with all the original Blinkenlights.

Project status: the injection mold is being produced now and the kit is planned for August...

This has been a three-year project, as Real Life Interference played up. But it is close to getting done now, and the world really needs more 36-bit mainframe class computers for home use.

But the injection mold design is done, the circuit boards work, and the software, of course, was already working: this has a Raspberry Pi running simh inside.

Before you get interested in the physical machine, have a look at [Lars]'s ITS project and [RCornwell]'s PDP-10 simulators. That's the most interesting bit ;)

  • 1 × Light panel PCB
  • 1 × Switch panel PCB
  • 1 × Raspberry Pi
  • 1 × MCP23017 16 extra IO pins
  • 1 × UDN2981 Driving 16 LEDs with extra oomph

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  • Done! (Mostly)

    Oscarv05/02/2023 at 22:19 1 comment

    Today the final prototype went through evaluation with the injection mold maker. There are some imperfections in this CNC-cut prototype, but they will be taken care of in the mold. I can't wait for the first samples to come back from the manufacturer. Alas, that will take 8 weeks or so. 

    Isn't she pretty? And just wait what this machine can do running ITS!

    So - today was a good day!

  • An injection mold proved inevitable

    Oscarv04/21/2023 at 23:16 0 comments

    It has been nearly three years since my last update here! But in the mean time, the software is pretty much done (famous last words), we've been playing a lot with ITS and all its graphics fun (multi-player mazewar, spacewar, it really is amazing how much software there is to play with on a PDP-10. See here)

    Although I promised myself never, ever, to do an injection mold again, that proved to be inevitable. So here is the CNC-cut prototype that will go into production in the coming weeks:


    Two molds, actually. A bottom, and a top part. To get all of the curves of the original properly made, I ended up needing professional help. The risk of cutting expensive injection molds with mistakes was too high, and 3D modeling the slight oddities of the 1966 original was also a bit beyond my skills.

    New PCBs have been spun to fit precisely in this case:

    126 LEDs, and...

    ... 74 switches. This is a big beast!

    To be continued soon. Or join the PiDP-10 Google Group if you want to follow progress more closely.

  • It blinks!

    Oscarv03/05/2020 at 18:17 0 comments


    The PCBs are soldered up (minus the switches, but they do work) and the PiDP-10 started to do its first blinkies. Admittedly, it still thinks it is a PDP-8 with a novel panel layout (I used modified pidp8i software for testing), but blinkies nevertheless.

    As it turns out, the new-to-me MCP23017 GPIO chip is really easy to control. Just a few lines of code; and the speed of the I2C bus is OK for this application. That was one concern: 24 bits of I/O a few hundred times per second, with enough time in-between to light up the LEDs in the multiplexing routine. I had to up the I2C clock on the Pi, but that was easy too. Everything is easy with a Raspberry Pi. Sometimes.

    Hopefully, the switch panel cover gets through Customs soon. Then, I have a complete demo machine :)

    Now on to modifying Richard Cornwell's KA10 simulator, so the machine can start to feel its 36 bits of simulated power! Oh, and soldering 72 switches. A chore I'd better get used to.

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Augusto Baffa wrote 04/22/2023 at 14:30 point

Hi Oscar, this is amazing! Could u please post the size of it in cm (w x h x d)? I need to reserve space on my bookshelf next to the PiDP-8 and PiDP-11 :D

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billp wrote 12/24/2021 at 18:37 point

I'm trying to remember... The DEC System 10's that Tymshare had in Cupertino had a PDP-11/? and a DEC Tape to boot the 10 and as a console system. That was pre-ARPAnet split days. Tymshare had a BBN IMP in it's Cupertino data center.

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rjbetterini wrote 11/27/2021 at 04:02 point

Alright!   I cut my teeth learning PDP-10 Assembler  freshman year  '73-74.  By the next year I was hacking TOPS10  Beta, on a KA of course

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Andrew Wasson wrote 09/16/2020 at 21:56 point

This is yet another amazing project. I'm still tinkering with my 2015, first run PiDP 8 and looking at the PiPDP 11 with envy. Now you've really gone and done it with this PDP 10 replica. This is such a lovely looking device. Digital Corp sure did have some great designers on staff. 

Did you ever get the switch plate panel that was lost in transit? I'm really looking forward to seeing more of this as you get the lights blinking and the switches switching.


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finn wrote 08/03/2020 at 02:13 point

That is one nice project.  I managed a KA-10 weekends '72-'73 and installed a CS dept.'s KL-10 in '76.  PDP-10s were the foundation of the ARPANET and Internet.  Serious hacker history there.  POPJ P, JFFO and hexadecimal ... bah.

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Peabody1929 wrote 03/07/2020 at 23:25 point

What is the project name at OSH?  I would like to take a look at the boards.

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Arduino Enigma wrote 02/26/2020 at 06:09 point

Nice! You are on a roll!!!

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Dan Maloney wrote 02/26/2020 at 01:43 point

That panel looks amazing! Of course it helps to have source material with as much style as the DEC machines had. 

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