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(operating system)
/muhl'tiks/ MULTiplexed Information and Computing Service. A time-sharing operating system co-designed by a consortium including MIT, GE and Bell Laboratories as a successor to MIT's CTSS. The system design was presented in a special session of the 1965 Fall Joint Computer Conference and was planned to be operational in two years. It was finally made available in 1969, and took several more years to achieve respectable performance and stability.

Multics was very innovative for its time - among other things, it was the first major OS to run on a symmetric multiprocessor; provided a hierarchical file system with access control on individual files; mapped files into a paged, segmented virtual memory; was written in a high-level language (PL/I); and provided dynamic inter-procedure linkage and memory (file) sharing as the default mode of operation. Multics was the only general-purpose system to be awarded a B2 security rating by the NSA.

Bell Labs left the development effort in 1969. Honeywell commercialised Multics in 1972 after buying out GE's computer group, but it was never very successful: at its peak in the 1980s, there were between 75 and 100 Multics sites, each a multi-million dollar mainframe.

One of the former Multics developers from Bell Labs was Ken Thompson, a circumstance which led directly to the birth of Unix. For this and other reasons, aspects of the Multics design remain a topic of occasional debate among hackers. See also brain-damaged and GCOS.

MIT ended its development association with Multics in 1977. Honeywell sold its computer business to Bull in the mid 1980s, and development on Multics was stopped in 1988 when Bull scrapped a Boston proposal to port Multics to a platform derived from the DPS-6.

A few Multics sites are still in use as late as 1996.

The last Multics system running, the Canadian Department of National Defence Multics site in Halifax, Nova Scotia, Canada, shut down on 2000-10-30 at 17:08 UTC.

The Jargon file 3.0.0 claims that on some versions of Multics one was required to enter a password to log out but James J. Lippard <>, who was a Multics developer in Phoenix, believes this to be an urban legend. He never heard of a version of Multics which required a password to logout. Tom Van Vleck <> agrees. He suggests that some user may have implemented a 'terminal locking' program that required a password before one could type anything, including logout.

Usenet newsgroup: news:alt.os.multics.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


(MULTiplexed Information and Computing Service) Developed at MIT and Bell Labs in the mid-1960s, MULTICS was the first timesharing operating system. It was also one of the first to implement symmetric multiprocessing. Used on GE's mainframes, which were absorbed into the Honeywell product line, MULTICS was later acquired by Bull.
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References in periodicals archive ?
The tiger team penetrated Multics and modified the manufacturer's master copy of the Multics operating system itself by installing a trap door: computer instructions to deliberately bypass the normal security checks and thus ensure penetration even after the initial flaw was fixed.
The Multics system kept a protected audit record of access, and the tiger team's unauthorized accesses were recorded.
The basis of the Award today is largely for my work on two pioneering time-sharing systems, CTSS [5, 6] and Multics [7, 9].
Let me turn now to the development of Multics [12].I will be brief since the system has been documented well and there have already been two retrospective papers written [3, 4].
So one of the tensions that went on for years was between the old batch-processing product line, and the new potential product, Multics, which was obviously a competitor.
They suddenly had to abandon Multics and revert either to the GE batch system GECOS or go back to other things.
"Corbato also led the development of Multics Multiplexed Information and Computer Service), a joint effort of Project MAC, Bell Telephone Laboratories, and the General Electric Co.
"CTSS and Multics stand out not only as operating systems per se but as important early examples of large-scale software engineering.
b The term process was borrowed from chemical engineering by the designers of the Multics system in the 1960s and is used interchangeably with the term task.
As a graduate student and faculty member at MIT, Schroeder worked on protection and security in computer systems, and on the Multics project.
Multics uses a similar mechanism for authenticating jobs submitted from a card reader: The job goes into a holding directory and is not run until user logs on and says to run it.

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