Multics 843 entries
15 Jul 2024

Glossary - U

Glossary of Multics acronyms and terms. Entries by Tom Van Vleck ([THVV]) unless noted.

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Multics site: University of Birmingham Computer Centre [UBCC] (Birmingham, England). 1983-1989. Four-processor DPS 8/70M, 28MB main memory, 6GB disk/drum storage, later upgraded to 5 CPUs with 8K cache.

Multics site: University of Calgary [UC] (Calgary, Alberta, Canada). 1978-1993. Had 5 CPUs. Perigon was a UC spinout company that took over Multics maintenance in the 80s. UC site history.

[RR] See also the Honeywell User News article about the sale.

(or UDD, user_dir_dir) Alternate names of the directory >user_dir_dir, whose subdirectories are project directories, whose subdirectories in turn are users' home directories. Compare PDD.

Unique identifier. Each segment has a unique identifier. The Multics UID generator is initialized by the clock reading at boot time and cannot generate more than one UID per microsecond.

Universal Interface Module. Feature designed but never implemented for 645 Multics.

UK file transfer & RJE

UK mail & network addressing

UK Transport Service

Costs extra. Some Multics software was not "bundled" with the hardware purchase, but instead had an additional charge. Typically there would be several prices: a large amount for a one-time paid-up license, or an initial fee and then a monthly license charge. This practice, of unbundling software and leasing it to the customer for a monthly fee, was introduced by IBM about 1970, and represented a radical shift in computer finance. Multics took to it reluctantly. It led to complications, since we had to avoid dependencies from standard software on unbundled products: for example, we couldn't use MRDS to store accounting data and produce reports. Unbundled software was stored in >system_library_unbundled, also called >unb.

[BSG] Since division of function by sharing of programs in a single large address space is one of the basic features of Multics, unbundling threatened this fundamental design goal. For example, Emacs could not rely on the "good" mail system, because it might not be there. Major improvements to functionality were relegated to options available for a price, and old, inadequate, embarrassingly obsolete tools could not be phased out. The inevitable transition from the age of software supplied with hardware to that of the competitive software vendor is at the heart of it, though. Emacs was one of the first unbundled products.

unclaimed signal
If a signal is raised, and the runtime cannot find a condition handler for it, it searches for a handler for "unclaimed_signal."

Universal Network Control Program. This GCOS-oriented terminal I/O subsystem ran on a DN355. Honeywell communications software. Multics could use it instead of MCS.

Article: Multics Communications and Networking.

[BSG] The character _, ASCII 137 (octal). Multics was one of the first systems to support file and function names longer than six or eight upper-case characters, and names such as make_segs_paged instead of MKSGSPGD were something of a novelty. The now-ubiquitous EmbeddedLeadingCaps style not having been loosed upon the world yet, underscores (always called that) were used throughout to delimit multi-word names.

One common use of underscore was as a trailing suffix for "system routines", an attempt to separate the potential user file and function namespaces. Hence, system-supplied API files (including deciduous supervisor segments) had names like bound_sss_active_ and bound_lisp_interpreter_ ("bound" means that the binder had been used to make these segments). Often, the segment name of a system API doing the real work for a command was suffixed with an underscore, e.g., delete_ was the API to properly delete a user-ring segment. The underscore was pronounced in such cases (e.g., "delete underscore"), which caused massive confusion about the spelling of the PL/I runtime support interface bound_ ("bound underscore", which checked bounds) and left one wondering if "delete underscore" deleted underscores.

Today's faddish leading underscores and multiple underscores were almost never employed by Multics. Underscores evolved into something of a Multics fetish/trademark, and occasionally even things like "Holy Underscore!" could be heard in the halls of CISL. (BSG, commissioned by Dick Snyder)

unique name
See shriek name.

university customers
See Arizona State, Avon Universities (Bristol & Bath), Brunel, Birmingham, CICB (Bretagne), CICG (Grenoble), CICRP (Paris), CICT (Toulouse), CICL (Lille), Cardiff, Calgary, Loughborough, MIT, Mainz, Nancy, Oakland, St. John's, University of Southwestern Louisiana, and Virginia Tech.

Operating system done at Bell Laboratories by Ken Thompson and Dennis Ritchie after BTL left the Multics team. Story: UNIX and Multics.

[BSG] PL/I language construct. UNSPEC is a pseudovariable and builtin function that treats its argument as an untyped word. As such it defeats type safety. Use of UNSPEC was prohibited in system code without permission from technical management.

Note, however, that PL/I does not type pointers (unlike C, which does), and "illegal" aliasing of storage via this means was trivial to achieve (although it played havoc with the compiler's optimizer).

upgraded directory
Directory with a higher AIM classification than its parent.

(1) A person registered on a project. Each user has a home directory. Per-user usage accounting is kept in the user's PDT entry.

(2) Also used casually to refer to a logged-in user process, or to the address space of a process.

User Control
Subsystem that handled login, user registration, projects, and so on.

[DMW] The standard process input I/O switch that commands normally read from. It is connected to the SYSIN file in PL/I.

[DMW] The standard I/O switch that can be assumed to be connected to the user process's control device (e.g., the user's terminal for interactive processes; the absin and absout segments for absentee processes) -- even if user_input and/or user_output have been redirected.

[DMW] The standard process output I/O switch that commands normally write to. It is connected to the SYSOUT file in PL/I. The attachment of this switch can be manipulated using such commands as file_output, terminal_output, and revert_output.

US Geological Survey. Multics customer. Three sites: Menlo Park CA, Reston VA, and Denver CO, from 1977 to 1986. See the USGS site history.

One program they used on the USGS systems was called HYPOELLIPSE/Multics, a computer program for determining local earthquake hypocentral parameters, magnitude, and first-motion pattern,.

[RR] Announcement (163K) in the Honeywell Printout of the USGS sale.

University of Southwestern Louisiana [USL] (Lafayette, LA). Multics customer 1975-1990. One of the first university Multics sales after MIT. USL had a swamp on campus with real alligators. They used Delta Data 4000's (video terminals) as terminals. See the USL site history. Now known as the University of Louisiana at Lafayette.