| Open SIMH | |
| Developer: | Robert M. Supnik |
| Released: | 1993 |
| Operating System: | Windows, Linux, macOS, FreeBSD, OpenBSD, NetBSD, OpenVMS |
| Programming Language: | C |
| Platform: | x86, IA-64, PowerPC, SPARC, ARM |
| Genre: | Hardware virtualization |
| License: | BSD-style licenses |
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.[2] 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.[3]
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.[4]
SIMH emulates hardware from the following companies.