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

IACL

[BSG] InitialACL. The successor to theCACL scheme, The initial ACL is a "default ACL" used as the ACL for new segments in adirectory (there is a separate "Directory IACL" for new subdirectories). From that point on, changes to the IACL have no effect on already extant segments -- access is determined by a segment's ACL alone.

idiotic

TheEPL compiler produced spectacularly bad code for some kinds of structure references.Jim Gimpel andDon Wagner looked at these problems and divided declarations into "synchronous," "asynchronous," and "idiotic" references, depending on whether an array of items was naturally word-aligned, was some submultiple of word-aligned, or was incommensurate with the word size. For example, an array of 37-bit items is idiotic, an array of 36-bit items is synchronous, and an array of 9-bit items is asynchronous. The EPL compiler was modified to tag all references with this classification, in a comment, in the generatedEPLBSA code. An early version of theKST had an idiotic declaration, and each reference to an element of it generated more than a whole page of assembly code from a single EPL statement.

idle process

[BSG] Multics creates a dedicated process for every CPU, all of whose code and data arewired. Called theidle process for that CPU, thescheduler gives a CPU to its idle process when there is nothing else for that CPU to do, i.e., no other process for it to run, so it can be so that every CPU is running one and only one process at any time. A ward of both birth and death, a CPU's idle process is the place where it is started whendynamic reconfiguration adds it to the system, and where it goes when it is to be deleted. Making thebootload CPU act in a fashion consistent with this (cf. Adam's navel in classic art) is a major prestidigitation oftraffic controlinitialization. The idle process flashed the CPU accumulator lights;Noel Morris made it flash the lights like a railroad crossing;Paul Green changed it to rotate the lights like a string of pearls, rolling one bit at each dispatch into it. The heart of the idle process's code is a DIS (Delay until Interrupt Signal) instruction.

IFAD

Integrated Firmware and Diagnostics. This tape was distributed with Multics. It contained firmware for multiprogrammed controllers (MPCs) and hardware diagnostics. T&D modules on the IFAD tape were loaded into>ldd>firmware withdeckfile_manager and placed on the MST so that online T&D could use them.

ifd

InterpretFDUMP. Multics tool written byBernie Greenberg in LISP that looked at aBOS FDUMP, interpreted its contents, and allowed inspection of system data structures. Inspired bySteve Webber'sol_dump. Althoughifd was never a product (in part because of its being written in an "unofficial language",MacLisp), it enjoyed widespread use. Replaced byanalyze_multics (azm).

illegal

[BSG] For a while, official Honeywell Multics documentation policy tried to make the use of the termillegal illegal -- if an opcode or command was "not recognized as valid" in a certain circumstance or ever but still lawful in Massachusetts and Arizona, it wasinvalid, but notillegal.

IMFT

Inter Multics File Transfer.

IML

Installation Maintained Library, stored in>iml.

IMP

Interface Message Processor. This machine, a Honeywell 516 running code provided by BBN, connected Multics to theARPANet.

IMU

Information Multiplexer Unit. A later, programmable version of theIOM. Supported in MR12.0.

IN

Industrial Nucleonics. Multics customer 1977-1991, located in Columbus, OH. Produced industrial process controllers and measurement instrumentation such as thickness gauges. Used Multics as a software factory forLevel 6 minicomputers. Controlled 35 Columbus, Ohio paper mills. Later called AccuRay Corporation, later bought by ASEA Brown Boveri.

[RR] Story:about the Industrial Nucleonics sale. Article:Software Factory Backs Up Pulp and Paper Mill, IEEE Computer, 1978.

info seg

Thehelp command prints out information from segments with the suffix.info, called info segments. The system info segments are kept in a specialdirectory whose pathname I forget. Thecheck_info_segs command checks the date modified of segments in this directory, and can perform a specified action on files modified since a date contained in a user profile segment. There was also a facility calledinfo created byCharlie Clingen in the early 70s, which printed out information from a tree-structured document.

inhibit

[BSG] Bit 28 (big-endian) of every645 and6180 instruction is labeled "inhibit", and preventsinterrupts,connectfaults, and timer runouts after this instruction (or pair on the6180). On the 645, the inhibit bit was only obeyed inmaster (privileged) mode. On the 6180, user programs can indeed use it, although there is no facility inPL/I to turn it on or off, and multi-CPU systems somewhat reduce its efficacy. A timer in the 6180 CPU limits the length of inhibit to so-many contiguous microseconds; if the timer runs out, the CPU takes alockupfault.

initialization

[BSG] Software mechanisms by which the Multicssupervisor is loaded and started from theboot tape and the system brought up.

initializer

First process created when Multics is booted. This process is manufactured at system startup by patching the system tables to make it appear that a process is running. The initializer process then completes Multics startup and runs theanswering service andmessage coordinator.

initiate

[BSG] Map into an address space and optionally assign areference name. Said of a segment. Also "to make a segmentknown" (to a process). To make the supervisor call (or as a side-effect ofdynamic linking) that associates a segment number with a file in thefile system by making an entry in a process'sKST. From that point on, references to that segment number become references to that segment, the fundamental illusion of the MulticsVirtual Memory. On Multics, instead of opening files, a user initiatessegments, and all the rest is magic .

INNPPP

Multics site: "Institut National de Physique Nuclèaire et de Physique des Particules" (Paris, France). 1983-1988.

[Daniel Bois] It is a Center of fundamental research in Nuclear Particles. Nothing to do with the Atomic Bomb neither Electricity. They are brains doing advanced studies on Particles.

[THVV] Founded in 1971. Formerly called Institut National Nucléaire et Physique des Particules de Paris.

[Daniel Bois] Now they are based in Lyon, which bring the subject of what have they done with the last P of INNPPP ? I do not know ...

INRA

Multics site: Institut National de la Recherche Agronomique [INRA] (Jouy en Josas, France), near Paris. 1980-1985.

INRIA

Multics site: Institut National de la Recherche en Informatique et en Automatique [INRIA] Three sites: Rocquencourt (79-85), Rennes (82-88), and Valbonne (Sophia-Antipolis), France (81-86). The Sophia site had one CPU and shared the machine room withCERAM.

[Daniel Bois] In Rocquencourt there has been one system from 1978 to about 1985 and then two Multics configuration, sometimes merged between INRIA and Bull. Complicate, isn't ?

INSEE

The French Minestère of Finances had three Multics sites for the Institut National de la Statistique et des Etudes Economiques, in Paris (81-84), Aix (80-84), and Lille (80-84).

[Daniel Bois] For typical MRDS applications and Time-Sharing usage. Basically the three sites ran the same configuration and applications. INSEE is a huge administration and they have seven computer sites altogether. First IBM customer in France.

Intellect

Natural language database query product from Artificial Intelligence Corporation (AIC) written in 1977. GeneratedMRDS queries. The lead guy was Dartmouth Prof. Larry Harris.

interactive message

Facility for sending one-line messages between users, including the commandsaccept_messages,defer_messages,delete_message,immediate_messages,[last_message],[last_message_time],[last_message_sender],send_message,send_message_acknowledge,send_message_silent andsend_message_express.Info segment forsend_message command

A logged-in user can enable this facility to cause messages to type out on the user'sterminal as soon as they arrive. The initial version of this facility was written byBob Frankston: it used shared memory segments writeable by everyone (with access coordinated by a simple lock) and anevent call channel that woke the process up and caused the message to print.

When ring-1message segments were introduced, the interactive message facility was rewritten to pass the messages securely in the user'smailbox.

A feature of theI/O daemon allows a user to request an interactive message from the printer daemon when output is printed, giving the physical printer selected and the print job sequence number.

interlace

[BSG] Technique of placing alternate word-pairs or word-quads of the system's physical memory (core) address space in alternateSCUs, to allow instructions accessing blocks of memory to overlap memory access. The CPUs andGIOCs/IOMs were capable of doing this, by means of a queue in theirPort Logic.

interrupt

[BSG] The645 /6180 CPU has a separate set of 32 interrupt vectors andfault vectors. Interrupts are always generated external to the processor, by the System Control Unit (SCU), in which the interrupt might have been "set" by another processor or the I/O box (seeGIOC,IOM). Interrupts are only recognized during instruction-pair fetches, not in mid-instruction. The interrupt mask is not in the processor, but in the port on the SCU to which the processor is connected. Inter-processor, or even looped-back, interrupts generated by processors are used to take processors on and off the system, crash or shutdown the system, and sendIPS signals to running processes. SeeSCAS.

ioa_

Standard Multics output formatter, ancestor toC printf, invented byStan Dunten as part ofBOS, and then made the basic output call for all standard programs.

IOCT

I/O Command Translator. In645 Multics, a generalized system for managing I/O.

I/O daemon

The I/Odaemon process runs all the printers and card equipment. It manages print queues and notifies users when it has done something for them. There were multiple priority queues for daemon requests, and different charges for each queue.

IOI (ioi_)

[BSG] I/O Interfacer. A unique facility in6180 Multics that allows any user granted the appropriate access to actually run the physical I/O of hardware devices directly to and from his or hersegments. IOI relies on the protection (base and bounds) registers ofIOM channels, and page control services for temporarily locking pages incore atabsolute, contiguous addresses as required for such use. Theprinter and backupdaemons as well asOn-line T & D use it. One ofNoel Morris's proudest masterpieces.

IOM

Input/Output Multiplexer. The6180 architecture's replacement for the645 system'sGIOC, except that IOMs didn't have terminal channels, so each system had aDN355 attached to the IOM to handle terminal I/O.

I/O module

[AG91] Program that processes input and output requests directed to a given switch. It may perform operations on other switches, or call the supervisor.

ios_

[BSG] I/O Switch. The original model forUnixstreams.ios_ mapped "stream" names into what are now called method tables by string lookup on each call. The table for each switch was the set of entry points of aDIM. Among the supported operations were synchronous and asynchronous reads and writes and controls, and the ability to define one stream as a synonym (i.e., front) for another. Replaced byiox_.

IOSIM

I/O Switch Interface Module. Seeiox_.

I/O switch

[AG91] Path in the I/O system through which information is sent.

IOTC

I/O Table Compiler. In 645 Multics, a tool for generating device descriptions for theIOCT.

iox_

[BSG] I/O Exchange. the MR1.0 follow-on toios_.iox_ combined the performance-directed move to referencing stream method tables by pointer as opposed to string name with a redefinition of the set of methods to more exactly map the repertoire ofPL/I I/O. As part of the package, some capabilities, such as asynchronous I/O, were lost, a change many saw as gratuitous and ill-advised. As a result, a vestigialios_ had to be kept around indefinitely to support the asynchronousARPANetDIMs.iox_ DIMs are calledIOSIMs.iox_ was the work ofDon MacLaren andMax Smith.

[THVV] SomeSIPB members referred toiox_ asHoneywell Brain Damage.

IPC

(1) Information Processing Center. MIT organization that ran the campus computer center. Part of theIPS organization. See theMIT Site History for more information.

(2) Inter-Process Communication. The facility for interprocess queueing and transmission ofwakeups and associated 72-bit data through a system queue.

IPR

(1) Independent Project Review. AGeneral Electric andHoneywell management process, in which people from outside a project would study it and report the risks.

(2) Illegal Procedure. Subclass of6180 processorfaults.

IPS

(1) Information Processing Services. MIT organization, next higher assembly toIPC, also included various other campus computing facilities such as Nuclear Science computers.

(2) Interprocess Signal. An asynchronous interrupt caused by another (privileged) process.

IPTO

ARPA Information Processing Techniques Office. Funded Multics development atProject MAC in the 1960s.

IRIA

Initial name ofINRIA.

IRT

Multics site: Institut de Recherche des Transports, Arcueil, France, near Paris. 1980-1986.

ISL

[DGRB] The ISL (InterSystemLink) hardware and software, by means of which files could be transferred directly between GCOS and Multics, was developed at STC.

ISOLTS

Isolated OnLine Test System. Online CPU diagnostics extracted from the FED diagnostic tape run byTOLTS. SeeAU77,Multics Online Test and Diagnostics Reference Manual.

[CAnthony] ISOLTS runs the GCOS code on a misconfigured 2nd CPU with a private 128KW memory block at location 0 in absolute mode; the test suite would run on any GCOS machine.

ISOLTS is built by reading the GCOS generated test suite tape into a library segment; when the test is running it intercepts the test suite attempts to read tests for the test tape and copies the test from the library segment into the private memory. The CGOS test code has no idea that Multics is out there.

[BushJA] I wrote the ISOLTS wrapper in the late 70s. ISOLTS is a wrapper for theGCOS based test suite. It is mainly aMME fault catcher which resolves the MME operands and performs the appropriate Multics system calls to satisfy them.

ISOT

Internal Static Offset Table. A per-process table that defines the location of theinternal static section for each procedure segment. SeeLOT.

iteration

The Multicsshell supports iteration over command arguments. For example, you can say

delete (a b c d).fortran

and this is expanded by the shell into

delete a.fortran
delete b.fortran
delete c.fortran
delete d.fortran

Seecommand language.

ITS

[BSG] (1) Indirect To Segment. 635/645/6180 indirect words contain a "further indirection tag", which allows for iteration of the indexing/indirection process after the address in the word has been picked up. The Multics processors added a feature whereby theappending unit watches the pike as these words come by, and if this "further indirection" field of an even-addressed word contains octal 43 ("ITS"), hijacks it before it even gets to theCU, interpreting its "address" field as asegment number (of theTPR) and passing on the odd word of the pair on to the control unit in its place. The net effect is that the word-pair can be viewed as a segment-word "pointer pair", a pointer to a location in two-dimensional virtual memory, and this pair of words, referred to as an "ITS pair" or "ITS pointer", is the standard Multics pointer format. On the 6180, aring number (seeTRR) was added. Both processors had instructions to storepointer registers in this format.

(2) Incompatible Time Sharing (a pun onCTSS, the Compatible Time-Sharing System), a PDP-10 operating system built by theMIT Artificial Intelligence Laboratory in the '60s and 70s, which was an intellectual source of ideas relating toEmacs,video, and networking.