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.

History

SIMH was based on a much older systems emulator called MIMIC, which was written in the late 1960s at Applied Data Research. 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. 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.

Emulated hardware

SIMH emulates hardware from the following companies.

Advanced Computer Design

AT&T

BESM

Burroughs

Control Data Corporation

Data General

Digital Equipment Corporation

GRI Corporation

Hewlett-Packard

Honeywell

Hobbyist projects

IBM

Intel

Interdata

Lincoln Labs – MIT Research Lab

Manchester University

MITS

Norsk Data

Royal-Mcbee

Sage Computer Technology

Scientific Data Systems

SWTPC

Systems Engineering Laboratories

Xerox Data Systems