SIMH

Open SIMH
Original authorRobert M. Supnik
DeveloperThe Open SIMH Project
Release1994; 32 years ago (1994)
Written inC
Operating systemWindows, Linux, macOS, FreeBSD, OpenBSD, NetBSD, OpenVMS
Platformx86, IA-64, PowerPC, SPARC, ARM
TypeHardware virtualization
LicenseMIT License
Websiteopensimh.org
Repositorygithub.com/open-simh

SIMH is a free and open source, multi-platform multi-system emulator. It was developed by Bob Supnik, a former DEC engineer and DEC vice president.

History

SIMH was based on a much older systems emulator called MIMIC, which was written in the late 1960s at Applied Data Research. It was a minicomputer simulator created by Mike McCarthy, Len Feshkens, and Bob Supnik that ran on a PDP-10.

The SIMH project began in 1993 and the first version was released by Supnik in 1994. It then transformed from a one-person project to a collaborative effort coordinated on GitHub.

In May 2022, the MIT License of SIMH version 4 on GitHub was unilaterally modified by a contributor to make it no longer free software, by adding a clause that revokes the right to use any subsequent revisions of the software containing their contributions if modifications that "influence the behavior of the disk access activities" are made. As of 27 May 2022, Supnik no longer endorses this version 4 on his official website for SIMH due to these changes, only recognizing the "classic" version 3.x releases.

On 3 June 2022, the last revision of SIMH not subject to this clause (licensed under BSD licenses and the MIT License) was forked by the group Open SIMH, with a new governance model and steering group that includes Supnik and others. The Open SIMH group cited that a "situation" had arisen in the project that compromised its principles. Open SIMH is governed by a Steering Group that includes Supnik, Clem Cole, Richard Cornwell, Paul Koning, Timothe Litt, and Seth Morabito.

The forked V4 stream is currently being developed at the Open SIMH GitHub. The "classic" version continues to be maintained, with version 3.12-5 released on 16 July 2024, and is available as a tagged branch of Open SIMH.

Emulated hardware

Version 6 Unix for the PDP-11, running in SIMH
Version 7 Unix for the PDP-11, running in SIMH
"4.3 BSD UNIX" from the University of Wisconsin, on a simulated VAX.

SIMH emulates hardware from the following companies.

Advanced Computer Design

  • PDQ-3

AT&T

BESM

Burroughs

Control Data Corporation

Data General

Digital Equipment Corporation

GRI Corporation

Hewlett-Packard

Honeywell

IBM

Intel

  • Intel systems 8010 and 8020

Interdata

Lincoln Labs – MIT Research Lab

Manchester University

MITS

Norsk Data

Royal-Mcbee

Sage Computer Technology

  • Sage II

Scientific Data Systems

SWTPC

Systems Engineering Laboratories

  • SEL-32 both Concept-32 and PowerNode systems

Xerox Data Systems

References

  1. 1 2 "About the Open SIMH project". Open SIMH. Retrieved 23 October 2026.
  2. 1 2 Supnik, Bob (2015). Walden, David (ed.). "The Story of SimH". IEEE Annals of the History of Computing. 37 (3). IEEE Computer Society: 78–80. Bibcode:2015IAHC...37c..78S. doi:10.1109/MAHC.2015.67.
  3. ↑ Burnet, Maxwell M.; Supnik, Robert M. (1996). "Preserving Computing's Past: Restoration and Simulation" (PDF). Digital Technical Jounral. 8 (3). Digital Equipment Corporation: 23–38. ISSN 0898-901X. Retrieved 21 October 2026.
  4. ↑ "SIMH FAQ" (PDF). Computer Simulation and History. 6 May 2019. Retrieved 23 October 2026.
  5. ↑ "simh repo: Add top level COPYRIGHT and LICENSE files · simh/simh@ce2adce". GitHub. Retrieved 4 June 2022.
  6. ↑ "simh@groups.io | Announcing the Open SIMH project". 3 June 2022. Retrieved 3 May 2026.
  7. ↑ "Computer Simulation and History". Computer Simulation and History. Retrieved 21 October 2026.
  8. ↑ "Altair Other Operating Systems". schorn.ch. Retrieved 30 April 2026.

Further reading