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From Wikipedia, the free encyclopedia
Developer(s)Robert M. Supnik
Initial release1993[1]
Stable release
3.12-3[2] 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
Websitesimh.trailing-edge.com Edit this at Wikidata

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, and has been in development in one form or another since the 1960s.


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.[4]

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.[5]

Emulated hardware[edit]

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[edit]

  • PDQ-3




Control Data Corporation[edit]

Data General[edit]

Digital Equipment Corporation[edit]

GRI Corporation[edit]



Hobbyist projects[edit]



  • Intel systems 8010 and 8020


Lincoln Labs – MIT Research Lab[edit]

Manchester University[edit]


Norsk Data[edit]


Sage Computer Technology[edit]

  • Sage II

Scientific Data Systems[edit]


Systems Engineering Laboratories[edit]

  • SEL-32 both Concept-32 and PowerNode systems

Xerox Data Systems[edit]


  1. ^ a b c "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 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.
  5. ^ "simh@groups.io | Announcing the Open SIMH project". 2022-06-03. Retrieved 2022-06-04.
  6. ^ "Altair Other Operating Systems".

External links[edit]