Computer Simulation and History
This site documents SimH, a simulator for historic computer
systems, as well as papers and reflections on the history of computing.
SimH (History Simulator) is a collection of simulators for historically
significant or just plain interesting computer hardware and software from the past.
The goal of the project is to create highly portable system simulators
and to publish them as open-source software on the Internet, with freely available copies
of significant or representative software.
This site contains the "classic" version of SimH, the 3.X stream. It
includes all of the simulators I wrote or maintain, as well as
the current releases of J. David Bryan's HP simulators. It also has
a collection of papers and software kits that are applicable to all
versions of SimH.
The V4 stream is substantially enhanced and contains many additional
simulators. It can be found on GitHub under the name
The source code in both V3 and (Open SimH) V4 is licensed under
an "MIT-style" open-source license. Contributions to either stream
are welcome if (and only if) they include this style of open-source license.
SIMH is a highly portable, multi-system simulator.
Download the latest sources and documentation
for SIMH V3.12-2, updated
25-Apr-2022. The change history can be found in the sim_rev.h header
file. Older releases can be found here.
- Download the latest sources, documentation, and software kits
for Dave Bryan's HP simulators.
Download PDF copies of the documentation
SIMH V3.x implements simulators for:
Data General Nova, Eclipse
Digital Equipment Corporation PDP-1, PDP-4, PDP-7, PDP-8, PDP-9, PDP-10 (KS10),
PDP-11, PDP-15 (and UC15), VAX11/780, VAX3900
GRI Corporation GRI-909, GRI-99
IBM 1401, 1620, 7090/7094, System 3
Interdata (Perkin-Elmer) 16b and 32b systems
Hewlett-Packard 2114, 2115, 2116, 2100, 21MX, 1000, 3000
MITS Altair 8800, 8080 only
Royal-McBee LGP-30, LGP-21
Scientific Data Systems SDS 940
Xerox Data Systems Sigma 32b systems
Also available is a collection of tools
for manipulating simulator file formats and for cross-assembling code for
the PDP-1, PDP-7, PDP-8, and PDP-11.
Release Notes for V3.12-2
This is the first official release of SimH 3.X in more than two years.
It includes numerous bug fixes and extensions to the individual simulators,
as well as a few major upgrades in capability:
See the detailed revision history in sim_rev.h for more details.
The magtape library (sim_tape.c) has been extended to allow the
inclusion of private metadata in SimH format tapes. The extension is backward compatible
to the previous format and is invisible to simulators that do
not need or support private metadata.
To support the tape format extension, there is a new version of
the mtdump utility. In addition to supporting the extended SimH
tape format, it supports P7B (Pierce 7bit) format for the first time.
Support for non-standard C compliant compilers has been dropped.
Papers on Simulation and Historic Hardware
Updated 05-Jun-2022 by Bob Supnik (simh AT groups DOT io - anti-spam encoded)