Emulating your very own DECSYSTEM-10 (PDP-10)

My first ‘professional’ programming job was on a DEC-10. I learned enough COBOL in high school that I managed to convince the Data Processing department at Texas State University to hire me as a programmer. They were an excellent IT shop and I learned lessons that have never left. However, I was paid less than minimum wage at the time, and within a year I move to a commercial shop where I doubled my pay. The DEC-10 was replaced by a VAX system within a few years and I never saw one again.

The DEC-10 was an influential system in its time. It was one of the early time-sharing systems and was installed in many universities. Bill Gates and Paul Allen used its 8080 emulator to write their first version of BASIC. Many influential games were written on it.


A few years ago I was researching something or another and stumbled across a DEC-10 emulator. I had some free time so I decided to figure out how to get one running for myself. Although I had written code for a DEC-10 I never acted as an operator. I had no idea how to get one running to the point where I could login and play with it.

You can find the PDP-10 emulator at


You also need a pre-built system (O/S installed into a hard drive). Go to


and download TOPS-10 7.03 Distribution R1.4 ( two rp06 pack images)

Once you have the parts you need to get the system up and running. Here are the notes I made to myself when I was learning how to operate the system. These notes not only include boot up/shut down but also using SOS to edit files, running batches, operating the printer, tape drives, etc.

My DEC-10 Notes

Once the DEC-10 is running, you can telnet into it:


If you take the time to build this emulation and get it running, you will find that TOPS-10 has many similarities to MS-DOS. I expect the early microcomputer O/S’s were influenced by this machine.

Last year I went with a friend to the Living Computer Museum in Seattle to find almost certainly the last running DEC-10 in the world. Paul Allen decided he didn’t want this (and other) systems to disappear and has maintained a running DEC-10 there.

This is a pretty accurate representation (in terms of hardware being used) of the system I used:


This entry was posted in c-retro and tagged . Bookmark the permalink.

12 Responses to Emulating your very own DECSYSTEM-10 (PDP-10)

  1. octavios says:

    Hi, I just found your blog. very exciting stuff. I do not have operator knowledge either but I am going to try this out. thanks for posting this info

  2. octavios says:

    Hi Dan- what flavor of Linux did you use to install the emulator on?

  3. octavios says:

    ok. Looks like I got a new project 🙂 thank you Dan

  4. octavios says:

    So I followed your lead and did it via Windows. Ran pdp10.exe (simh) and followed your configuration instructions per “my-dec-10-notes.pdf” and could logon, run systat and everything!

    But I did have a small question – how did you telnet in – is there a particular port/name etc on your windows machine?

    • Dan TheMan says:

      Looking back at this, I was running the reflections terminal emulator which does not easily telnet into any port besides 23, so I’m fairly certain I just used straight telnet.

      To verify the port number, use netstat -a to see what ports are being listened to. One should be 23 (I’m assuming here you don’t have a telnet server on your system already).

      I suspect you will find 23 in the list. Then telnet into it. If you are running the emulator on the same system, use the local ip address:


      I don’t see it in my notes, but I vaguely recall being able to change the telnet port to something else in simh. If you don’t see port 23 open you should be able to find something in google about assigning telnet port for simh.

  5. octavios says:

    thanks Dan, appreciate the tip, all working now 🙂

  6. Gordon Zaft says:

    Hey, really enjoyed looking at this. My 2nd computer (1st was a PDP8 at my high school) was a DEC-10 at the University of Arizona that I spent a lot of time with. Good memories. Thanks!

  7. No, that’s not a very accurate representation. SIMH emulates a KS10, or DEC-2020. The machine in your picture is a KI10, or DEC-1070.

  8. Andrew says:

    Hello Dear All,
    Nice to comeback to the 80-90ths )))
    SIMH work good, bud I have one trouble how to start other games.
    I remember Empire perfect strategy game )))
    I finded it on classicempire.com, and special files for PDP-10 but unfortunately couldn’t start them with SIMH ((
    Please could you advise some ideas to play Empire with SIMH .
    Many thanks in advance!

    • Dan TheMan says:

      You would need to get the dec-10 simulation running, load all of the files via an editor or copy from paper tape, and then compile them. Looks like you need both the FORTRAN compiler and assembler to make that happen. Sounds like a fun challenge! Good luck!

  9. Andy Patterson says:

    I worked on DEC-System-10s for around 10 years. Worked for DEC as a software specialist. I wrote a real-time OS that ran on DOS. Used a lot of concepts I learned from TOPS-10. I implemented resource, event, and scheduling queues based on TOPS-10 internals. I added inter-task messaging and message queues. The basic task scheduling was from TOPS-10. TSR could open the OS interface and run concurrently with other tasks including a normal DOS forground application. A text windowing system was also available to background tasks. TOPS-10 was the most resistant OS to unauthorised access I have used.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.