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

Open SIMH

Developer(s)	Robert M. Supnik
Initial release	1993[1]
Stable release	3.12-3[2]  / 31 January 2023
Repository	github.com/open-simh/simh
Written in	C
Operating system	Windows, Linux, macOS, FreeBSD, OpenBSD, NetBSD, OpenVMS
Platform	x86, IA-64, PowerPC, SPARC, ARM
Type	Hardware virtualization
License	BSD-style licenses
Website	simh.trailing-edge.com

History

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

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

• 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^[6]

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