Multics (from Multiplexed Information and Computing Service) was an influential time-sharing operating system developed during the 1960s in a joint project by MIT's Project MAC, General Electric, and Bell Labs. Multics was commercialized by Honeywell and Groupe Bull for their mainframe hardware, reaching a peak of about 80 installations worldwide by the early 1980s. The last known Multics site running on real hardware was operated by the Canadian Department of National Defence and was shut down on October 30, 2000.

Although commercially disappointing, Multics enjoyed a reputation as a highly secure operating system. Multics developers pioneered a number of operating system concepts such as the hierarchical file system and system programming in a high-level language that were later popularized in the Unix operating system and have become standard in current operating systems.

The Living Computer's simulated Honeywell 6180 system runs Multics version MR12.6e. Watch Living Computers Multics system boot for the first time. The panel is real hardware originally used at the University of Michigan and interfaced to the simulated Honeywell 6180.

The Multics user environment will be very familiar to Unix-style shell users. In fact, many Unix shell command names were inspired by Multics commands.

Multics resolves meaningful command versus easy typing tradeoff by having it both ways: Every command has a long meaningful name with the most frequently used commands also given a short 2-3 character alias. (Unix developers tended to adopt the short command aliases and forget the meaningful names.) Multics commands are case-sensitive.

Multics documentation uses the term segment to refer to files.

Using Multics on the Multics Wiki is an excellent tutorial on basic Multics commands for new users.

Linux-to-Multics Command Mapping has a list of corresponding commands in Unix and Multics.

There are a differences between Unix and Multics that should be kept in mind:

• In Multics file specifications the greater-than character (>) is used as a directory separator instead of Unix's slash (/). The less-than character (<) is used to refer to the current working directory's parent directory instead of Unix's (..).
• Some command names are used in both Multics and Unix but have unrelated functions. For example, the command cd in Unix changes the current working directory, but in Multics creates a new directory (long form create_dir). (To change the current directory in Multics, use the command cwd (long form change_wdir).)

Get help on Multics with the help command, instead of man on Unix.

• qedx The Multics standard line-oriented text editor.
• Multics Emacs Extensible screen-oriented text editor.
• Multics TECO Arcane character-oriented text editor.

• Multics PL/I
• Multics Maclisp

• Multics - Wikipedia
• Multicians web site (The Multics Glossary contains a wealth of information and entertaining lore.)
• Multics Wiki
• Multics Repository at Stratus Technologies
• Bitsavers' PDF Document Archive - Honeywell > Multics