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."Preserving Computing's Past: Restoration and Simulation" Max Burnet and Bob Supnik, Digital Technical Journal, Volume 8, Number 3, 1996. SIMH was started in 1993 with the purpose of preserving minicomputer hardware and software that was fading into obscurity.
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. 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.
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.
Emulated hardware
SIMH emulates hardware from the following companies.
Advanced Computer Design PDQ-3
AT&T 3B2
BESM BESM-6
Burroughs B5500
Control Data Corporation CDC 1700
Data General Nova Eclipse
Digital Equipment Corporation Alpha PDP-1 PDP-4 PDP-7 PDP-8 PDP-9 PDP-10 PDP-11 PDP-15 VAX Family Systems MicroVAX I, VAXStation I MicroVAX II, VAXStation II MicroVAX 3900 VAX 11/730 VAX 11/750 VAX 11/780 VAX 8600
GRI Corporation GRI-909
Hewlett-Packard 2116 2100 21MX 3000
Honeywell H316 H516
Hobbyist projects N8VEM
IBM 650 701 704 1401 1620 1130 7010 7070 7080 7090/7094 System/3
Intel Intel systems 8010 and 8020
Interdata 16-bit series 32-bit series
Lincoln Labs – MIT Research Lab TX-0
Manchester University Baby, or SSEM
MITS Altair 8800 both Intel 8080 and Zilog Z80 versions
Norsk Data Nord-100
Royal-Mcbee LGP-30 LGP-21
Sage Computer Technology Sage II
Scientific Data Systems SDS 940
SWTPC SWTPC 6800
Systems Engineering Laboratories SEL-32 both Concept-32 and PowerNode systems
Xerox Data Systems Sigma
References
External links Computer Simulation and History Official site Additional VAX/MicroVAX models for SIMH Running VAX/VMS Under Linux Using SIMH Debian Package FreeBSD Port UNIX: Old School. Using SIMH to explore UNIX history - Matthew Hoskins SCSI tape drive emulation for the Raspberry Pi with support for SIMH tape image files