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.

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.^{[4] [5]}

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.^{[6] [7]}

SIMH emulates hardware from the following companies.

• 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