HOWTO learn to program PDP-11 assembler with a modern PC and SIMH

Jason sez, "Inspired by DePauw University's videos, I wanted to explore how I can simulate my own PDP-11 and run the programs from the video. So, I did it and I'm in the process of posting how on my blog. Later on I hope to add to the series and explore the areas the videos didn't have time for, like running Star Trek. Right now, you can get a walkthrough of how to compile the SIMH simulator and toggle in a Hello, World program. Enjoy!"

Programming Your PDP-11: Part 0: (Thanks, Jason!)



  1. A college friend’s high school had a DEC PDP-8. The kids got excited about programming the thing, and wanted to diddle around with the interpreter for the language they were using. (FORTRAN? BASIC? I forget the details.)

    At great difficulty they obtained the source.

    The comments were in Portuguese . . .

  2. My friend Steve’s dad ran an insurance office with one of these back in the day – Steve and I were both initiated into the world of computer games by playing Trek on those terminals. I wonder if there is a PDP-11 port of Doom (with ascii graphics of course – but that’s already been done with Doom).

  3. All these PDP-11 posts just might come in handy for me…we actually have one sitting in the back of our lab.

    Since I’ve been good, though they let me use the Windows 3.11 box.

  4. Simulating the PDP-11 is wonderful, but the real deal would be simulating the KSR-33 terminals complete with papertape read/write, the mechanical bell (ctrl-G) and the banging shaking rumbling chugging quaking that it makes at full tilt.

  5. I don’t have access to a KSR-33 anywhere to do this with, but it’s possible to do. SIMH will handle serial IO easily. There are a few sites that accept telnet connections to SIMH emulation sessions.

    Spare Time Gizmos sells a replica PDP-11 front panel interface. The KY11 Interface connects a spare front panel to a PC with an emulator using RS-232. Just because I know you’re dying to toggle all those switches yourself!

  6. I learned to program (COBOL at first) on a VMS11/780 starting in 1980. I missed the PDP-11 and its punch cards by a single term. I never learned DEC Assembler but I did learn IBM Assembler that first year, a fact I’ve been at pains to conceal for fear that someone will insist that I do it for a living.

  7. Actually, this is not a bad idea. If you’re interested in learning assembler programming, the 11’s architecture is a nice straightforward one to wrap your head around… almost RISC in its simplicity.

    (I did a fair amount of ’11 hacking when I was a student, including some device driver debugging that did require working through the front panel.)

  8. I switched majors from Computer Science to Psychology back in the early 80s after being forced to program a PDP-11 assembly simulator in Pascal for a required class for my major. The instructor was pathetically horrible, and unfortunately taught several of the ‘gatekeeper’ classes in the department that were required passes to graduate.

  9. My first job out of a college I got because I’d learned and used PDP-11 assembly language.

    But no, the PDP-11 instruction set is in no way RISC, with its large set of addressing modes. Everything is very regular and orthogonal, which makes it easy, but the 32-bit version of the PDP-11, which carried its design principles further, was the VAX, and RISC was born as a rebellion against the VAX.

  10. I envy people who have time for this retro stuff–maybe someone needs my Kaypro 2 or Commodore 64.
    SUBHAN-Were you at UCSD by any chance? The PDP-11 assy. language class was equally hideous & in 1980 we did PASCAL on networked Apple IIs!

  11. ~5 years ago I took a digital systems course where we programmed PDP-ish assembly in a PC emulation app. I’m not sure if it was a VM or just interpreted the assembly language programs. The language almost made a perverse kind of sense after a while. Then they made us do quicksort, and ever since, I’ve been allergic to burning days reinventing the wheel…

  12. we use a version of this computer to run the the system that inspects the reactor integrity in CANDU nuclear reactors. Its not as bulky as the one pictured and it has a 5 1/2 inch floppy drive.

  13. I have been an electronic technician at the US Postal service since 1980. Many of our sorting machines were controlled by the PDP 11 until 1999.

  14. Nostalgia City. I wrote advertising for the PDP-11, and even the PDP-8/e. The mid-range 11’s were the size of small refrigerators, or of a bank of small refrigerators.

    I wonder how many of the older SF writers cut their technological teeth on these guys.

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