This page has my notes relating to building and using Open-SIMH, particularly in the context of Windows machines.
The website for Open-SIMH is here -> https://opensimh.org/
The official Open-SIMH repository can be found here -> https://github.com/open-simh/simh
That official Open-SIMH repository has source code only. It does not contain any Windows executables.
Pre-built Open-SIMH executables
Downloading and compiling the Open-SIMH emulators on a Linux machine is fairly simple. Windows is not so straight forward.
Thankfully, Terri Kennedy has created a repo with pre-built executables for Windows (as well as other platforms).
Terri’s repo is available here -> https://github.com/Terri-Kennedy/Open-SIMH-Unofficial-Builds
Here is a local copy of the Windows builds from Terri’s repo as at 08-OCT-2025 (based on Open-SIMH GitHub commit 6e9324e09f4f364346310de34849077c986c29f2″) for the Altair, AltairZ80, pdp8 and pdp11 emulators, together with Terri’s notes (including the Windows build process) -> Windows Open-SIMH Builds as at 08-OCT-2025.
Building Windows executables using Cygwin
Before Terri’s pre-built executables became available, I experimented with making my own builds using Cygwin.
Here’s the process I followed to build a Windows executable version of an Open-SIMH emulator under Windows 11 Pro:
- Download and install cygwin. Just go with the defaults except add make, cmake, gcc and vim
- download the open-simh package and unzip it on your PC. I chose to put the files at C:\open-simh-simh-29d3900
- Run cygwin by clicking on “Cygwin64 Terminal” in the start menu, or running “Cygwin.bat” in your cygwin64 directory.
- You can see the mounted directories in cygwin by typing the “mount” command”. You should see that C: has been mounted as /cygwin/c
- In cygwin, change from your cygwin home directory into the open-simh directory (for me that was done using the command “cd /cygdrive/c/open-simh-simh-29d3900”). Check that you can see the SIMH files there using the “ls -l” command
- Build the PDP-8 simulator using the command “make pdp8”. This will take a minute or so. The resultant windows executable will be located in the BIN directory under your open-simh directory
- You can now execute the pdp8 simulator in the cygwin environment using the “./pdp8” command
- Exit cygwin using the “exit” command
You will also now be able to execute the PDP-8 windows executable in the native Windows environment, provided you have edited your PATH environment to add the cygwin64\bin directory (so Windows finds the “cygwin1.dll” file when you run “pdp8.exe”). To do this I went into “Settings” from the start button, then searched for “environment variables” in the “Find a setting” search bar and selected the result “Edit the system environment variables”
The above example is to build the pdp8 simulator on (and to run under) Windows 11 Pro.
I also used the same Cygwin environment to assemble palbart from David’s site. It can be found here -> https://www.pdp8online.com/ftp/software/palbart/. It assembles under Cygwin with the command “gcc -o palbart palbart.c”.