ZIMH Historical Computer Simulator

ZIMH (which stands for "ZIMH Implements Machine History"), is a software emulator for important computer systems and peripherals from the history of computing. It provides a mechanism by which modern users can run and experience what it was like to use old computers that have not been made in many decades, or use software that was intended for systems that no longer exist.

(It is of course possible to also use the ZIMH framework to simulate more recent or even current machines, though this has not been the typical use case.)

ZIMH is a hard fork of SIMH, a simulator created by Bob Supnik and extended over many years by the SIMH team. We are grateful to Bob and the SIMH contributors for all of their work over the years. Without their efforts, none of this would be possible.

The development track of ZIMH is substantially different from that of the original SIMH project. In particular, this project is pursuing:

• A much higher velocity of development
• An extensive, automated, in-tree test suite sufficient to allow for that high velocity development
• Extensive modernization and cleanup of the codebase
• Progressive conversion of the implementation to Rust
• Uplift of the simulators into a machine-readable architecture specification language that can be automatically lowered into executable code

ZIMH has already accomplished the following goal:

• Conversion of the documentation into text-based, non-Microsoft Word-based formats

Conversations with the upstream team indicated that they would almost certainly not be interested in adopting the kinds of changes planned here. Accordingly, this fork is being developed independently and we have changed the name of the project to ZIMH.

This project is made available under an X11 style license; see LICENSE.txt for details.

For a current catalog of the simulator targets in this tree, see docs/manual/simulators.md.

Version Numbers

ZIMH uses calendar versioning.

Release versions have the form YYYY.M.D, for example 2026.4.24.

If more than one release is made on the same day (not very often), an additional numeric component is appended, for example 2026.4.24.1.

The version number indicates release date, not API compatibility. Compatibility-affecting changes are documented in the release notes.

Repository Layout

The repository contains:

• src/: shared core, runtime, and reusable in-tree components
• simulators/: source trees for specific machine simulators
• docs/: project-level, historical, and legacy-format documentation
• third_party/: vendored or externally-derived code
• tools/: build helpers, CI support, and developer utilities
• tests/: shared test infrastructure and test data

Build entrypoints visible at the top level:

• CMakeLists.txt
• Makefile
• cmake/
• vcpkg.json

More detail is in docs/project/layout.md.

PLEASE NOTE

Do not contribute material taken from github.com/simh/simh unless you are the author of the material in question; that repository is not open source.