Article · Wikipedia archive · Last revised Jul 12, 2026

SIMH

SIMH is a free and open source, multi-platform multi-system emulator. It is maintained by Bob Supnik, a former DEC engineer and DEC vice president, based on a much older systems emulator called MIMIC.

Last revised
Jul 12, 2026
Read time
≈ 3 min
Length
627 w
Citations
10
Source
Wikipedia ↗
Open SIMH
DeveloperRobert M. Supnik
Initial release19931
Stable release
3.12-32 Edit this on Wikidata / 31 January 2023
Written inC
Operating systemWindows, Linux, macOS, FreeBSD, OpenBSD, NetBSD, OpenVMS
Platformx86, IA-64, PowerPC, SPARC, ARM
TypeHardware virtualization
LicenseBSD-style licenses
Websiteopensimh.org Edit this on Wikidata
Repository

SIMH is a free and open source, multi-platform multi-system emulator. It is maintained by Bob Supnik, a former DEC engineer and DEC vice president, based on a much older systems emulator called MIMIC.

History

SIMH was based on a much older systems emulator called MIMIC, which was written in the late 1960s at Applied Data Research.1 SIMH was started in 1993 with the purpose of preserving minicomputer hardware and software that was fading into obscurity.1

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 behaviour of the disk access activities" are made.3 As of 27 May 2022, Supnik no longer endorses version 4 on his official website for SIMH due to these changes, only recognizing the "classic" version 3.x releases. The classic version continues to be maintained, with version 3.12-5 released on 16 July 2024.45

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.67

Emulated hardware

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

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

  • GRI-909

Hewlett-Packard

Honeywell

Hobbyist projects

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

References

  1. "Preserving Computing's Past: Restoration and Simulation" Max Burnet and Bob Supnik, Digital Technical Journal, Volume 8, Number 3, 1996.
  2. "Release 3.12-3". 31 January 2023. Retrieved 24 February 2023.
  3. "simh repo: Add top level COPYRIGHT and LICENSE files · simh/simh@ce2adce". GitHub. Retrieved 2022-06-04.
  4. "SimH "Classic"". simh.trailing-edge.com. Retrieved 3 May 2026.
  5. "SimH "Classic"". simh.trailing-edge.com. Retrieved 2022-06-04. The V4 GitHub repository has been placed under a modified license that effectively makes it closed source. It will no longer be referenced here.
  6. "simh@groups.io | Announcing the Open SIMH project". 2022-06-03. Retrieved 3 May 2026.
  7. "simh@groups.io | Announcing the Open SIMH project". 2022-06-03. Retrieved 2022-06-04.
  8. "Altair Other Operating Systems". schorn.ch. Retrieved 2026-04-30.
External links