Multics > Library
15 Jul 2024

Multics Source

Multics Source History

Multics development began at MIT, GE and Bell Labs in 1966, using MIT's CTSS as the source repository. Early versions of the source were not preserved. When Multics became self-hosting in 1967, the development repository was on the MIT Multics machine, and system releases were named MSS, Multics Standard System. After Multics became a Honeywell product in 1973, standard "MR" release numbers were assigned by the Phoenix Multics Development Center, which maintained packaged and shipped releases from its development repository. Here is a brief history of source related events: see the History page for more.

  • 1969 Multics Standard Systems 1.0 2.0, 3.0, 4.0, 5.0 from MIT/GE
  • 1969 Multics Standard Systems 6.0 - 13.0 from MIT/GE
  • 1970 Multics Standard Systems 14.0 - 15.0 from MIT/GE
  • 1970 Multics Standard Systems 18.0 from MIT/GE
  • 1974 Multics Standard Systems 22.0 from MIT/GE
  • 1974 Multics Release MR 1.0 from PMDC
  • 1974 Multics Release MR 2.0, 2.1, 2.2, 3.0 from PMDC (see Dates for more details)
  • 1976 Multics Standard System 22.0 from MIT/GE: New Storage System
  • 1976 Multics Release MR 3.1, 4.0, 4.0.1, 5.0 from PMDC
  • 1977 Multics Release MR 6.0 from PMDC
  • 1978 Multics Release MR 6.1, 6.5, 6.5a from PMDC
  • 1979 Multics Release MR 7.0, 7.0a, 7.0b from PMDC
  • 1980 Multics Release MR 8.0, 8.2 from PMDC
  • 1981 Multics Release MR 9.0 from PMDC
  • 1982 Multics Release MR 9.1, 10.0 from PMDC
  • 1983 Multics Release MR 10.1 from PMDC
  • 1985 Multics Release MR 11.0 from PMDC: B2 Rating
  • 1985 Multics developent canceled by Bull HN
  • 1986 Multics Release MR 12.0 from PMDC
  • 1988 Bull outsourced Multics maintenance to ACTC
  • 1988 Multics Release MR 12.2 from ACTC
  • 1989 Multics Release MR 12.3 from ACTC
  • 1990 Multics release MR 12.4 from ACTC
  • 1992 Multics release MR 12.5 from ACTC
  • 2000 last Multics site (DND) shut down
  • 2007 Bull releases source of MR 12.5 + Y2K fixes to public hosting at
  • xxxx bootable Release tape images for MR 12.3, 12.4 and 12.5 available at
  • 2014 DPS8M Simulator available for Windows, Unix, Mac on
  • 2017 DPS8M Simulator 1.0 and MR 12.6f available
  • 2019 DPS8M Simulator 2.0 available
  • 2019 Adam Sampson created multics-history-repo at GitLab with MR12.3, MR12.4, MR12.5, MR12.5-MIT, MR12.6
  • 2021 MR12.7 available
  • 2021 MR12.7 repository from Dan Cross and Doug Wells available
  • 2022 Adam Sampson added MR12.7 to GitLab multics-history-repo
  • 2022 DPS8M Simulator 3.0 available on GitLab
  • 2023 DPS8M Simulator 3.0.1 available
  • 2023 MR12.8 available
  • 2024 Multics Source Browser available in GitLab.

Multics Source Browser

Jeffrey Johnson has created a browser for the Multics source for MR12.8 in GitLab.

Multics DPS8M Simulator

The DPS8M simulator is available for download from GitLab. It simulates a Multics system on Windows, macOS, or Unix.

(2023) Multics Release 12.8 is now available for use on the simulator. This release is based on the Bull software, with changes to fix bugs and enhance usability. Eric Swenson was the release coordinator. Changes are discussed on the SourceForge mailing lists dps8m-users, dps8m-developers, and on the Multicians mailing list.

(2021) Dan Cross and Doug Wells created a Release 12.7 GitHub repository for the release. This archive was created by Doug using mxload; it replaces Multics archive files with subdirectories. You can easily download the entire source of Multics to your own computer.

(2022) Adam Sampson created a repository on GitLab with the sources of all releases we've been able to locate. This Multics History Repo was constructed by parsing the history comments in source files automatically converted to Git commits. See for details.

How to Download the Entire Source Code of a Multics Release

Eric Swenson In order to get your own copy of the source of Multics from any of these repositories,

  1. Install a copy of the git tool on your computer.
  2. In a web browser, visit the source repository.
  3. Copy the repository URL to your clipboard.
  4. In a terminal window on your computer, execute git clone with that URL.

You'll get the head (e.g. MR12.7) checked out and in your directory. This will download about 170 MB of source files. Each original .archive file will be represented as a directory of files.

You can switch to other releases using git checkout TAG. You can list the tags with git tag -list.

Using Multics to develop Multics

Gary Dixon I still prefer to look at Multics source using Multics tools on a simulated Multics. Availability of library_pathname (and library descriptor tools in general), peruse_crossref, print_bind_map, plus ability to recompile sources to get full object listings are big advantages for investigating any serious questions.

Documentation for Development Tools

Documentation for Multics library maintenance commands, in the form of .info segments, is available from Adam Sampson's GitLab repository:

Development Example from Eric Swenson

(to be added to Multics wiki)

Honeywell/Bull Multics MR12.5 Source of Multics Hosted at MIT

(2007) A complete copy of the final Bull HN source code of Multics release MR 12.5 is now available at, thanks to Bull.
An index to these source files is available on this site. (05/23/01, 444K).
This index shows all 5877 source files from Multics release MR 12.5.

Selected source from 1985

To view nine annotated examples of source code from the MIT source archive for about 1985, see Selected Multics Source.