SIMH

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What SIMH is

SIMH is a free collection of portable simulators for historically significant or otherwise interesting computer hardware and software. It runs on Linux, macOS, and Windows, and publishes open-source simulator code alongside freely available copies of representative software. SIMH V3.x lists 36 supported systems, including Data General Nova and Eclipse, DEC PDP and VAX machines, IBM, HP, Honeywell, Interdata, and the MITS Altair 8800. The project also provides utilities for manipulating simulator file formats and cross-assembling programs for PDP-1, PDP-7, PDP-8, and PDP-11 systems. Open SIMH V4 is an enhanced stream with additional simulators, available through GitHub. The latest listed V3 source and documentation release is SIMH V3.12-5, updated July 16, 2024; its notes describe mostly bug fixes and Chaosnet support for PDP-10 and PDP-11 simulators. Software kits are available for several simulated systems, although some carry licenses that restrict use. Documentation, help guides, and a SimH users’ mailing list provide support. V3 and Open SIMH V4 source code uses an MIT-style open-source license.

Who it suits

SIMH suits users studying historical systems, preserving older software, or experimenting with machine simulators on Linux, macOS, or Windows. Its tools also serve people cross-assembling code for listed PDP systems.

What it does well

Free and open-source simulator collection
Supports Linux, macOS, and Windows
36 listed supported systems
Includes file-format and cross-assembly tools
Documentation and users’ mailing list available

What to know first

Some software kits have use-restricting licenses
HP 2100 implementation omits 1000 L/A-Series machines
V3.12-5 is mainly a bug-fix release

Verdict

SIMH offers broad historical-system coverage with portable source, software kits, and development utilities. Its V3 and Open SIMH V4 streams give users different simulator sets, while individual kit licenses require attention.

Facts from SIMH's own pages

Build requirements: The HP simulator source distributions are written in portable C, and the page says no additional libraries are needed to build them. · simh.trailing-edge.com, 11 Oct 2026
Downloads: The HP simulator page offers source distributions and precompiled 32-bit Windows executables for Windows XP and later. · simh.trailing-edge.com, 11 Oct 2026
Founded: 1993 · simh.trailing-edge.com, 28 Sept 2026
HP platform support: The HP simulator pages state that those simulators run on common PC and Mac platforms running Windows, Linux, FreeBSD, or macOS. · simh.trailing-edge.com, 11 Oct 2026
HP simulator scope: The HP simulator page says its HP 2100 implementation does not model the 1000 L/A-Series machines. · simh.trailing-edge.com, 11 Oct 2026
License: The V3 and Open SIMH V4 source code is licensed under an MIT-style open-source license. · simh.trailing-edge.com, 11 Oct 2026
Machine coverage: The V3 release lists simulators for systems including Data General, DEC, IBM, Interdata, HP, Honeywell, MITS Altair, and others. · simh.trailing-edge.com, 11 Oct 2026
No commercial pricing: The site describes SIMH as open-source software and offers downloads, with no paid plans or prices stated on the pages reviewed. · simh.trailing-edge.com, 11 Oct 2026
Project goal: The project aims to create highly portable system simulators and publish them as open-source software with freely available copies of significant or representative software. · simh.trailing-edge.com, 11 Oct 2026
Purpose: SIMH is a collection of simulators for historically significant or otherwise interesting computer hardware and software. · simh.trailing-edge.com, 11 Oct 2026
Release: The site's latest listed V3 source and documentation release is SIMH V3.12-5, updated July 16, 2024. · simh.trailing-edge.com, 11 Oct 2026
Release changes: SIMH V3.12-5 release notes say the release is mostly bug fixes and adds Chaosnet support to the PDP-10 and PDP-11 simulators. · simh.trailing-edge.com, 11 Oct 2026
Simulator coverage: SIMH V3.x includes simulators for systems including Data General Nova and Eclipse, DEC PDP and VAX systems, IBM systems, HP systems, and the MITS Altair 8800. · simh.trailing-edge.com, 11 Oct 2026
Software kits: The site lists software kits for several simulated systems, and says some kits have licenses that restrict their use. · simh.trailing-edge.com, 11 Oct 2026
Software tools: The site also provides tools for manipulating simulator file formats and cross-assembling code for the PDP-1, PDP-7, PDP-8, and PDP-11. · simh.trailing-edge.com, 11 Oct 2026
Support: The site points users to documentation, help guides, and a SimH users' mailing list for support and questions. · simh.trailing-edge.com, 11 Oct 2026
Tools: The site offers tools for manipulating simulator file formats and cross-assembling code for PDP-1, PDP-7, PDP-8, and PDP-11 systems. · simh.trailing-edge.com, 11 Oct 2026
V3 release: The site lists SIMH V3.12-5 as the latest V3 source and documentation release, updated 16 July 2024. · simh.trailing-edge.com, 11 Oct 2026
V4 stream: The site says the enhanced V4 stream contains additional simulators and is available on GitHub as Open-SimH. · simh.trailing-edge.com, 11 Oct 2026

Where SIMH stands on Freedom251

Multi-System Emulators#50 of 54