CAPS-11 is the Casette Programming System for the PDP-11. The manual is available at Bitsavers, binaries can be found at SimH.

The manual contains instructions how to assemble the system from source, the source code should be available somewhere.

I have disassembled the code, but annotated source would be really useful. I have googled around and not found anything.

(I am 100% pdp11 novice writing pdp11 emulator from scratch for kicks)

  • 2
    It would help if you'd say for what you'd like some source code ... there's plenty of PDP-11 stuff around. If you want to understand PDP-11 assembly, there's also plenty of documention around.
    – dirkt
    Jun 27, 2020 at 6:28
  • @dirkt caps-11 is an operating system for PDP-11
    – JeremyP
    Jun 27, 2020 at 8:01
  • I think the answer is going to be no.
    – JeremyP
    Jun 27, 2020 at 8:05
  • 3
    I concur that the likely answer is 'no' (given bitsavers does not have it) but the question is now clear enough, if "needs clarity" was the reason to close. Voted to reopen.
    – dave
    Jun 27, 2020 at 17:34
  • 2
    @JeremyP happily the answer was 'yes'
    – pm100
    Jun 28, 2020 at 21:45

1 Answer 1


A guy named Lou Ernst on the Usenet group alt.sys.pdp11 mentioned that he had it with sources back in 2011:

Last night we finally got CAPS-11 running on our 11/04 with TA11/ TU60. Jack R. was given a set of original DEC CAPS-11 cassettes during one of his recent expeditions. These included bootable cassettes, object files, and all the sources. He mailed them to me, and I was able to recover the contents of these original 37 year old tapes on my TU60.

A person going by the name of "paramucho" comments that

I didn't know it was missing! I've had this V3.0 magtape distribution sitting a directory for a while now:


Described below as a TU10 distribution:


I tried to install on a simulated RL02 it tonight under SIMH. It boots up nicely and asks all the right questions, but after doing the badblk check all I get are disk errors and then tape errors (I can't get E11 to run on 64-bit Windows and my emulator doesn't do tapes).

The zip file linked contains a TU tape image. I poked around in it and there's plenty of readable ASCII but I couldn't identify whether or not it contains what you want. You'll probably have to mount it in an emulator or find tools for listing/extracting the files.

Update: It turned out that the guy in that thread who thought he had the same files had something else after all, so his links were of no use.

If not then some of the names and email addresses in that thread should lead you to somebody who can get you a copy.

Spoiler: OP did receive a copy from Lou!

  • 1
    Hm. For me it contains IAS30SYS.TAP, but it doesn't seem to be a SimH tape, at least. As for IAS, it looks like another operating system with at least some similarities to RSX. So I am not sure if the link is about CAPS-11. But nice find.
    – dirkt
    Jun 28, 2020 at 5:04
  • 1
    Lou says in another post that he's given it to the appropriate place for archiving, but not who that is. I suppose the PDP-11 people in the group would all know. Also of note, it comes up a couple of times in that thread that nobody could find the manual and that's the one piece that today is easy to find on the internet. Jun 28, 2020 at 5:15
  • 1
    Anything called IAS30SYS.TAP is surely an IAS 3.0 system tape. IAS is (loosely speaking) RSX-11D with timesharing support and the then-new Digital Command Language (DCL) as the primary UI, rather than MCR. It's a "large PDP-11" OS, at the opposite end of the spectrum from CAPS-11.
    – dave
    Jun 28, 2020 at 12:59
  • 2
    I contacted ernst and he supplied the full source code!! Is there a place for retro OS sources, I could load it there
    – pm100
    Jun 28, 2020 at 21:44
  • 2
    It would be nice to get it on bitsavers.org.
    – dave
    Jun 29, 2020 at 2:10

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