RSX11M+ on SIMH - A Quest for the Unique Blinking Lights of RSX

Parent Category: How-to's Category: Getting RSX11M+ running on SIMH Written by Administrator

First I’d like to provide a bit of background on my project that Jörg Hoppe made possible with his modified Simh and the Blinkenbus technology he and his colleagues have developed. I bought a DECsystem 570 front panel on ebay. This was a smaller front print PDP-11/70 that fit in two tall 19 inch racks.

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My goal was to run RSX11M+ on an emulator and have the reanimated display exhibit the idle light pattern that RSX systems produced on PDP-11s.


In the early 1980s, I saw the RSX pattern on a PDP-11/70 at a DEC office in Chicago where I was taking the RSX operating system internals course. The RSX light pattern starts from each side of the LEDs and moves to the center where it then explodes outward. This was a system with core memory that didn't need power to retain memory. If you pulled the plug and then reconnected the power, the operating system picked up where it left off. Users editing a file might loose a single key stroke, but there edited file was intact. That's the kind of reliability you need if you want to control a nuclear reactor. In fact, GE is looking for experienced RSX programmers (in 2013) for their nuclear control systems, if you have the background.

I looked at several projects on the internet that reanimated PDP-11 front panels and contacted Jörg who with his colleague Thomas Höffken (who created the I/O boards) provided everything that was needed. Jorge has provided excellent documentation on his Blinkenbus platform here and here on this site which I used to put the pieces together.

I did one thing differently than Jörg in making the connections from the three 40 pin ribbon cables that connect the front panel to the I/O board which was to use wire-wrapped connection between the I/O pins on the board and 40 pin wire wrap connectors which mate with the cables from the front panel.

blinkenboard wirewrap

 In this article however, I want to describe in detail how to obtain and build a customized RSX11M+ operating system for the finished project.


Building a multi-user PDP-11 operating system to use with Simh and a Blinkenboard is fairly straight forward. The most sophisticated PDP-11 operating system is RSX11M+ which runs particularly well on a PDP-11 with I/D space (11/44, 11/70, 11/73, 11/83. 11/84, 11/93). The last version of it (V4.6) was updated to be Y2K compatible so current dates work fine on it. You can find a bootable “baseline” disk image at:

Once you download and unzip this file you will have a .dsk file that you can use as a bootable RSX11M+ system on most emulated PDP-11s.

 I like using the PDP-11/93 for test work on Simh as it contains a TOY clock so you don’t have to keep typing in the date and time on boot. It can get the date/time from the linux system it is running on (Angstrom/Ubuntu). Also, I use a BeagleBone Black for the development work with Ubuntu on a 16GB microSD. For a BlinkenBone system you will need a Beagle Bone White, the BlinkenBus card and a BlinkenBus I/O board. I will have more on that topic in another article.



Download this file (appendix_a__getting_the rsx11m+_distribution.txt)Appendix A[Getting the RSX11M+ distribution]7 kB
Download this file (appendix_b__expanding_rsx11m+_baseline_disk.txt)Appendix B[Expanding RSX11M+ baseline disk]0.3 kB