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Multics ("Multiplexed Information and Computing Service") is an influential early
time-sharing In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and sof ...
operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, Android (operating system), Android and Mi ...

operating system
based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of the ACM, Vol. 17, 1984, pp. 365-375. It has been said that Multics "has influenced all modern operating systems since, from microcomputers to mainframes." Initial planning and development for Multics started in 1964, in
Cambridge, Massachusetts Cambridge ( ) is a city in Middlesex County, Massachusetts, Middlesex County, Massachusetts, and part of the Greater Boston, Boston metropolitan area as a major suburb of Boston. , it was the fifth most populous city in the state, behind Boston, ...
. Originally it was a cooperative project led by
MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, hi ...
(
Project MAC MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) is a research institute A research institute, research centre, or research center is an establishment founded for doing research. Research institutes may specialize in basic r ...
with Fernando Corbató) along with
General Electric General Electric Company (GE) is an American Multinational corporation, multinational Conglomerate (company), conglomerate incorporated in New York State and headquartered in Boston. Until 2021, the company operated through GE Aviation, aviat ...
and
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, ab ...
. It was developed on the
GE 645 The GE 645 mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as census, censuses, industr ...
computer, which was specially designed for it; the first one was delivered to MIT in January, 1967. Multics was conceived as a commercial product for General Electric, and became one for
Honeywell Honeywell International Inc. is an American public company, publicly traded, multinational corporation, multinational conglomerate (company), conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four are ...

Honeywell
, albeit not very successfully. Due to its many novel and valuable ideas, Multics has had a significant impact on computer science despite its faults. Multics has numerous features intended to ensure high availability so that it would support a computing utility similar to the
telephone A telephone is a telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: Greece Anyt ...

telephone
and
electricity Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physi ...

electricity
utilities A public utility company (usually just utility) is an organization that maintains the infrastructure Infrastructure is the set of fundamental facilities and systems that support the sustainable functionality of households and firms. Serving a ...
. Modular hardware structure and software architecture are used to achieve this. The system can grow in size by simply adding more of the appropriate resource, be it computing power, main memory, or disk storage. Separate
access control list In computer security Computer security, cybersecurity, or information technology security (IT security) is the protection of computer system A computer is a machine that can be programmed to carry out Sequence, sequences of arithmetic o ...
s on every file provide flexible information sharing, but complete privacy when needed. Multics has a number of standard mechanisms to allow engineers to analyze the performance of the system, as well as a number of adaptive performance optimization mechanisms.


Novel ideas

Multics implements a
single-level store Single-level storage (SLS) or single-level memory is a computer storage File:Maxell DVD-RW 4.7GB crop 20051120.jpg, A spindle of DVD-RWs Computer data storage is a technology consisting of computer components and Data storage device, record ...
for data access, discarding the clear distinction between
file File or filing may refer to: Mechanical tools and processes * File (tool) A file is a tool used to remove fine amounts of material from a workpiece. It is common in woodworking, metalworking, and other similar trade and hobby tasks. Most are ...
s (called ''segments'' in Multics) and ''
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process A business process, business method ...
memory Memory is the faculty of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exis ...
''. The memory of a process consists solely of segments that were mapped into its
address space In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwa ...
. To read or write to them, the process simply uses normal
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of individual electroni ...

central processing unit
(CPU) instructions, and the operating system takes care of making sure that all the modifications were saved to
disk Disk or disc may refer to: * Disk (mathematics) * Disk storage Music * Disc (band), an American experimental music band * Disk (album), ''Disk'' (album), a 1995 EP by Moby Other uses * Disc (galaxy), a disc-shaped group of stars * Disc (magazin ...
. In
POSIX The Portable Operating System Interface (POSIX) is a family of standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * St ...
terminology, it is as if every file were
mmap In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...
()
ed; however, in Multics there is no concept of ''process memory'', separate from the memory used to hold mapped-in files, as
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast t ...

Unix
has. ''All'' memory in the system is part of ''some'' segment, which appears in the
file system In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and soft ...
; this includes the temporary scratch memory of the process, its kernel stack, etc. One disadvantage of this was that the size of segments was limited to 256 kilowords, just over 1  MB. This was due to the particular hardware architecture of the machines on which Multics ran, having a
36-bit 36-bit computers were popular in the early mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks ...
word size and index registers (used to address within segments) of half that size (18 bits). Extra code had to be used to work on files larger than this, called multisegment files. In the days when one megabyte of memory was prohibitively expensive, and before large databases and later huge
bitmap In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...

bitmap
graphics, this limit was rarely encountered. Another major new idea of Multics was
dynamic linking In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwar ...
, in which a running process could request that other segments be added to its address space, segments which could contain code that it could then execute. This allowed applications to automatically use the latest version of any external routine they called, since those routines were kept in other segments, which were dynamically linked only when a process first tried to begin execution in them. Since different processes could use different search rules, different users could end up using different versions of external routines automatically. Equally importantly, with the appropriate settings on the Multics security facilities, the code in the other segment could then gain access to data structures maintained in a different process. Thus, to interact with an application running in part as a
daemon Daimon or Daemon (δαίμων: "god", "godlike", "power", "fate") originally referred to a lesser deity A deity or god is a supernatural being considered divinity, divine or sacred. The ''Oxford Dictionary of English'' defines deity as a G ...
(in another process), a user's process simply performed a normal procedure-call instruction to a code segment to which it had dynamically linked (a code segment that implemented some operation associated with the daemon). The code in that segment could then modify data maintained and used in the daemon. When the action necessary to commence the request was completed, a simple procedure return instruction returned control of the user's process to the user's code. Multics also supported extremely aggressive on-line reconfiguration:
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of individual electroni ...

central processing unit
s, memory banks, disk drives, etc. could be added and removed while the system continued operating. At the MIT system, where most early software development was done, it was common practice to split the
multiprocessor Multiprocessing is the use of two or more central processing units A central processing unit (CPU), also called a central processor, main processor or just Processor (computing), processor, is the electronic circuitry that executes Instruct ...
system into two separate systems during off-hours by incrementally removing enough components to form a second working system, leaving the rest still running the original logged-in users. System software development testing could be done on the second system, then the components of the second system were added back to the main user system, without ever having shut it down. Multics supported multiple CPUs; it was one of the earliest multiprocessor systems. Multics was the first major operating system to be designed as a secure system from the outset.Jerome H. Saltzer, "Protection and the Control of Information Sharing in Multics", in "Introduction to Multics", MAC TR-123, Project MAC, Cambridge, February 1974; pg. 2-41. Despite this, early versions of Multics were broken into repeatedly. This led to further work that made the system much more secure and prefigured modern
security engineering Security engineering is the process of incorporating security controls into an information system so that the controls become an integral part of the system’s operational capabilities. It is similar to other systems engineering activities in tha ...
techniques. Break-ins became very rare once the second-generation hardware base was adopted; it had hardware support for ring-oriented security, a multilevel refinement of the concept of master mode. A US Air Force tiger team project tested Multics security in 1973 under the codeword ZARF. On 28 May 1997, the American National Security Agency declassified this use of the codeword ZARF. Multics was the first operating system to provide a
hierarchical file system Hierarchical File System (HFS) is a Proprietary software, proprietary file system developed by Apple Inc. for use in computer systems running Classic Mac OS, Mac OS. Originally designed for use on floppy disk, floppy and hard disks, it can also b ...
, and file names could be of almost arbitrary length and syntax. A given file or directory could have multiple names (typically a long and short form), and symbolic links between directories were also supported. Multics was the first to use the now-standard concept of per-
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process A business process, business method ...
stack
stack
s in the
kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...
, with a separate stack for each security ring. It was also the first to have a command processor implemented as ordinary user code – an idea later used in the
Unix shell A Unix shell is a command-line interpreter or shell Shell may refer to: Architecture and design * Shell (structure)A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness ...
. It was also one of the first written in a high-level language (Multics
PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative Imperative may refer to: *Imperative mood, a grammatical mood (or mode) expressing commands, direct requests, and prohibitions *Imperative prog ...
), after the
Burroughs MCP The MCP (Master Control Program) is the proprietary {{Short pages monitorIBM_LinuxONE.html" ;"title="IBM z Systems z13. On the ... architecture since its inception. This scheme is unique in the industry, as it stores and retrieves compiler-define ...
system written in
ALGOL Algol , designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple star in the constellation A constellation is an area on the celestial s ...
.R. A. Freiburghouse
"The Multics PL/1 Compiler"
General Electric Company, Cambridge, Massachusetts, 1969.
The deployment of Multics into secure computing environments also spurred the development of innovative supporting applications. In 1975, Morrie Gasser of MITRE Corporation developed a pronounceable random word generator to address password requirements of installations such as the Air Force Data Services Center (AFDSC) processing classified information. To avoid guessable passwords, the AFDSC decided to assign passwords but concluded the manual assignment required too much administrative overhead. Thus, a random word generator was researched and then developed in PL1. Instead of being based on phonemes, the system employed phonemic segments (second order approximations of English) and other rules to enhance pronounceability and randomness, which was statistically modeled against other approaches. A descendant of this generator was added to Multics during Project Guardian.


Project history

In 1964, Multics was developed initially for the
GE-645 The GE-600 series was a family of 36-bit 36-bit computers were popular in the early mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer A computer is a machine that can be programmed to car ...
mainframe, a
36-bit 36-bit computers were popular in the early mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks ...
system. GE's computer business, including Multics, was taken over by Honeywell in 1970; around 1973, Multics was supported on the
Honeywell 6180 The Honeywell 6000 series computers were rebadged versions of General Electric General Electric Company (GE) is an American Multinational corporation, multinational Conglomerate (company), conglomerate incorporated in New York State and hea ...
machines, which included security improvements including hardware support for
protection ring In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study ...
s.
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, ab ...
pulled out of the project in 1969; some of the people who had worked on it there went on to create the
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast t ...

Unix
system. Multics development continued at MIT and General Electric. Honeywell continued system development until 1985. About 80 multimillion-dollar sites were installed, at universities, industry, and government sites. The French university system had several installations in the early 1980s. After Honeywell stopped supporting Multics, users migrated to other systems like Unix. In 1985, Multics was issued certification as a B2 level secure operating system using the Trusted Computer System Evaluation Criteria from the National Computer Security Center (NCSC) a division of the
NSA The National Security Agency (NSA) is a national-level intelligence agency An intelligence agency is a government agency A government or state agency, sometimes an appointed commission, is a permanent or semi-permanent organization in the m ...

NSA
, the first operating system evaluated to this level. Multics was distributed from 1975 to 2000 by
Groupe Bull Bull SAS (also known as Groupe Bull, Bull Information Systems, or simply Bull) is a French computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automaticall ...
in
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
, and by Bull HN Information Systems Inc. in the United States. In 2006, Bull SAS released the source code of Multics versions MR10.2, MR11.0, MR12.0, MR12.1, MR12.2, MR12.3, MR12.4 & MR12.5 under a
free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty ...

free software
license. The last known Multics installation running natively on Honeywell hardware was shut down on October 30, 2000, at the Canadian
Department of National DefenceDepartment of Defence or Department of Defense may refer to: Current departments of defence * Department of Defence (Australia) * Department of National Defence (Canada) * Department of Defence (Ireland) * Department of National Defense (Philippine ...
in Halifax, Nova Scotia, Canada.


Current status

In 2006 Bull HN released the source code for MR12.5, the final 1992 Multics release, to MIT. Most of the system is now available as
free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty ...

free software
with the exception of some optional pieces such as
TCP/IP The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A commu ...
. In 2014 Multics was successfully run on current hardware using an emulator. The 1.0 release of the emulator is now available. Release 12.6f of Multics accompanies the 1.0 release of the emulator, and adds a few new features, including command line recall and editing using the video system.


Commands

The following is a list of programs and commands for common computing tasks that are supported by the Multics
command-line interface A command-line interface (CLI) processes command COMMAND.COM is the default command-line interpreter A command-line interface (CLI) processes commands to a computer program in the form of lines of text. The program which handles the i ...
. * apl * ceil * change_wdir (cwd) *
cobol COBOL (; an acronym An acronym is a word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (lingui ...

cobol
*
copy Copy may refer to: *CopyingCopying is the duplication of information Information is processed, organised and structured data. It provides context for data and enables decision making process. For example, a single customer’s sale at a res ...
(cp) *
echo In audio signal processing Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves—longitudinal waves whic ...
*
emacs Emacs or EMACS (Editor MACroS) is a family of text editor A text editor is a type of computer program that edits plain text. Such programs are sometimes known as "notepad" software, following the naming of Microsoft Notepad. Text editors a ...
*
floor A floor is the bottom surface of a room or vehicle. Floors vary from simple dirt in a cave to many-layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the expected load ...
*
fortran Fortran (; formerly FORTRAN) is a general-purpose, compiled language, compiled imperative programming, imperative programming language that is especially suited to numerical analysis, numeric computation and computational science, scientific com ...

fortran
(ft) * gcos (gc) *
help Help may refer to: Arts, entertainment, and media Films * Help (2010 film), ''Help'' (2010 film), a Bollywood horror film * Help (2021 film), ''Help'' (2021 film), a British psychological thriller film * Help! (film), ''Help!'' (film), a 196 ...
* home_dir (hd) * if *
list A ''list'' is any set of items. List or lists may also refer to: People * List (surname)List or Liste is a European surname. Notable people with the surname include: List * Friedrich List (1789–1846), German economist * Garrett List (194 ...
(ls) *
login In computer security Computer security, cybersecurity, or information technology security (IT security) is the protection of computer system A computer is a machine that can be programmed to carry out Sequence, sequences of arith ...
(l) *
logout In computer security Computer security, cybersecurity, or information technology security (IT security) is the protection of computer systems and computer network, networks from information disclosure, theft of or damage to their com ...
* ltrim *
mail The mail or post is a system for physically transporting postcard A postcard or post card is a piece of thick paper or thin Card stock, cardboard, typically rectangular, intended for writing and mailing without an envelope. Non-rectangular s ...
(ml) *
pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, French ...
* pl1 * print (pr) * print_wdir (pwd) *
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed (printing), bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off ...
(rf) * rtrim *
sort Sort may refer to: * Sorting Sorting is any process of arranging items systematically, and has two common, yet distinct meanings: # ordering Order or ORDER or Orders may refer to: * Orderliness, a desire for organization * Categorization, t ...
* teco * trunc *
where Where may refer to: * Where?, one of the Five Ws in journalism * where (command), a shell command * Where (SQL), a database language clause * Where.com, a provider of location-based applications via mobile phones * Where (magazine), ''Where'' (ma ...
(wh) *
who The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United Nations and each other through the co-ordinating machinery of the Unit ...
* working_dir (wd)


Retrospective observations

Peter H. Salus, author of a book covering Unix's early years, stated one position: "With Multics they tried to have a much more versatile and flexible operating system, and it failed miserably". Quoting Peter Salus. This position, however, has been widely discredited in the computing community because many of Multics' technical innovations are used in modern commercial computing systems. The permanently resident kernel of Multics, a system derided in its day as being too large and complex, was only 135 KB of code. In comparison, a Linux system in 2007 might have occupied 18 MB. The first
MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, hi ...

MIT
GE-645 The GE-600 series was a family of 36-bit 36-bit computers were popular in the early mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer A computer is a machine that can be programmed to car ...
had 512 kilowords of memory (2 MiB), a truly enormous amount at the time, and the kernel used only a moderate portion of Multics main memory. The entire system, including the operating system and the complex
PL/1 PL/I (Programming Language One, pronounced and sometimes written PL/1) is a Procedural programming, procedural, imperative programming, imperative computer programming language developed and published by IBM. It is designed for scientific, engi ...
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
, user commands, and subroutine libraries, consisted of about 1500 source modules. These averaged roughly 200 lines of source code each, and compiled to produce a total of roughly 4.5 MiB of procedure code, which was fairly large by the standards of the day. Multics compilers generally optimised more for code density than CPU performance, for example using small sub-routines called ''operators'' for short standard code sequences, which makes comparison of object code size with modern systems less useful. High code density was a good optimisation choice for Multics as a multi-user system with expensive main memory. During its commercial product history, it was often commented internally that the Honeywell Information Systems (HIS) (later Honeywell-Bull) sales and marketing staff were more familiar with and comfortable making the business case for Honeywell’s other computer line, the Honeywell Level 6 , DPS 6 running General Comprehensive Operating System , GCOS. The DPS-6 and GCOS was a well-regarded and reliable platform for inventory, accounting, word processing, and vertical market applications, such as banking, where it had a sizeable customer base. In contrast, the full potential of Multics’ flexibility for even mundane tasks was not easy to comprehend in that era and its features were generally outside the skill set of contemporary business analysts. The scope of this disconnect was concretized by an anecdote conveyed by Paul Stachour, CNO/CSC:
When American Telephone and Telegraph was changing its name to just AT&T in 1983, a staffer from Honeywell’s legal department showed up and asked a Multician if he could arrange to have the name changed in all of their computerized documents. When asked when the process could be completed, the Multician replied, "It's done." The staffer repeated that he needed ''hundreds perhaps thousands'' of documents updated. The Multician explained that he had executed a global search and replace as the staffer was speaking, and the task was in fact completed.


Influence on other projects


Unix

The design and features of Multics greatly influenced the
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser Multi-user software is computer software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast t ...

Unix
operating system, which was originally written by two Multics programmers, Ken Thompson and Dennis Ritchie. Superficial influence of Multics on Unix is evident in many areas, including the naming of some commands. But the internal design philosophy was quite different, focusing on keeping the system small and simple, and so correcting some perceived deficiencies of Multics because of its high resource demands on the limited computer hardware of the time. The name ''Unix'' (originally ''Unics'') is itself a pun on ''Multics''. The ''U'' in Unix is rumored to stand for ''wikt:uniplex, uniplexed'' as opposed to the ''wikt:multiplex, multiplexed'' of Multics, further underscoring the designers' rejections of Multics' complexity in favor of a more straightforward and workable approach for smaller computers. (Garfinkel and Abelson cite an alternative origin: Peter Neumann at Bell Labs, watching a demonstration of the prototype, suggested the pun name UNICS – pronounced "eunuchs" – as a "castrated Multics", although Dennis Ritchie is said to have denied this.) Ken Thompson, in a transcribed 2007 interview with Peter SeibelPeter Seibel. Coders at Work: Reflections on the Craft of Programming. APress Publications, 2007. refers to Multics as "overdesigned and overbuilt and over everything. It was close to unusable. They [Massachusetts Institute of Technology] still claim it's a monstrous success, but it just clearly wasn't". On the influence of Multics on Unix, Thompson stated that "the things that I liked enough (about Multics) to actually take were the hierarchical file system and the shell — a separate process that you can replace with some other process".


Other operating systems

The Prime Computer operating system, PRIMOS, was referred to as "Multics in a shoebox" by William Poduska, a founder of the company. Poduska later moved on to found Apollo Computer, whose AEGIS and later Domain/OS operating systems, sometimes called "Multics in a matchbox", extended the Multics design to a heavily networked graphics workstation environment. The Stratus VOS operating system of Stratus Computer (now Stratus Technologies) was very strongly influenced by Multics, and both its external user interface and internal structure bear many close resemblances to the older project. The high-reliability, availability, and security features of Multics were extended in Stratus VOS to support a new line of fault tolerant computer systems supporting secure, reliable transaction processing. Stratus VOS is the most directly-related descendant of Multics still in active development and production usage today. The protection architecture of Multics, restricting the ability of code at one level of the system to access resources at another, was adopted as the basis for the security features of International Computers Limited, ICL's ICL VME, VME operating system.


See also

* Time-sharing system evolution * Peter J. Denning * Jack B. Dennis * Robert Fano – director of Project MAC at MIT (1963–1968) * Robert M. Graham (computer scientist) * J. C. R. Licklider – director of Project MAC at MIT (1968–1971) * Peter G. Neumann * Elliott Organick * Louis Pouzin – introduced the term ''shell'' for the command language used in Multics * Jerome H. Saltzer * Roger R. Schell * Glenda Schroeder – implemented the first command line user interface shell (computing), shell and proposed the first email system with Pouzin and Crisman * Victor A. Vyssotsky


References


Further reading

The literature contains a large number of papers about Multics, and various components of it; a fairly complete list is available at th
Multics Bibliography
page and on a second, briefe

(text format). The most important and/or informative ones are listed below. * Fernando J. Corbató, F. J. Corbató, Michael Schroeder, V. A. Vyssotsky
''Introduction and Overview of the Multics System''
(AFIPS 1965) is a good introduction to the system. * Fernando J. Corbató, F. J. Corbató, C. T. Clingen, J. H. Saltzer
''Multics – The First Seven Years''
(AFIPS, 1972) is an excellent review, written after a considerable period of use and improvement over the initial efforts. * J. J. Donovan, Stuart Madnick, S. Madnick
Operating Systems
is a fundamental read on operating systems. * J. J. Donovan
Systems Programming
is a good introduction into systems programming and operating systems.


Technical details

* Jerome H. Saltzer,
Introduction to Multics
' (MIT Project MAC, 1974) is a considerably longer introduction to the system, geared towards actual users. * Elliott Organick, Elliott I. Organick, ''The Multics System: An Examination of Its Structure'' (MIT Press, 1972) is the standard work on the system, although it documents an early version, and some features described therein never appeared in the actual system. * Victor A. Vyssotsky, V. A. Vyssotsky, Fernando J. Corbató, F. J. Corbató, R. M. Graham,
Structure of the Multics Supervisor
' (AFIPS 1965) describes the basic internal structure of the Multics kernel. * Jerome H. Saltzer,
Traffic Control in a Multiplexed Computer System
' (MIT Project MAC, June 1966) is the original description of the idea of switching kernel stacks; one of the classic papers of computer science. * R. C. Daley, Peter G. Neumann, P. G. Neumann,
A General Purpose File System for Secondary Storage
' (AFIPS, 1965) describes the file system, including the access control and backup mechanisms. * R. J. Feiertag, Elliott Organick, E. I. Organick,
The Multics Input/Output System
'. Describes the lower levels of the I/O implementation. * A. Bensoussan, C. T. Clingen, R. C. Daley,

', (Association for Computing Machinery, ACM SOSP, 1969) describes the Multics memory system in some detail. * Paul Green (engineer), Paul Green,
Multics Virtual Memory – Tutorial and Reflections
' is a good in-depth look at the Multics storage system. * Roger R. Schell, ''Dynamic Reconfiguration in a Modular Computer System'' (MIT Project MAC, 1971) describes the reconfiguration mechanisms.


Security

* Paul A. Karger, Roger R. Schell,
Multics Security Evaluation: Vulnerability Analysis
' (Air Force Electronic Systems Division, 1974) describes the classic attacks on Multics security by a "tiger team". * Jerome H. Saltzer, Michael Schroeder, Michael D. Schroeder,
The Protection of Information in Computer Systems
' (Proceedings of the IEEE, September 1975) describes the fundamentals behind the first round of security upgrades; another classic paper. * Michael Schroeder, M. D. Schroeder, D. D. Clark, J. H. Saltzer, D. H. Wells.
Final Report of the Multics Kernel Design Project
' (MIT LCS, 1978) describes the security upgrades added to produce an even more improved version. * Paul A. Karger, Roger R. Schell,
Thirty Years Later: Lessons from the Multics Security Evaluation
' (IBM, 2002) is an interesting retrospective which compares actual deployed security in today's hostile environment with what was demonstrated to be possible decades ago. It concludes that Multics offered considerably stronger security than most systems commercially available in 2002.


External links


multicians.org
is a comprehensive site with a lot of material *

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discusses numerous myths about Multics in some detail, including the myths that it failed, that it was big and slow, as well as a few understandable misapprehensions *

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Includes extensive overview of other software systems influenced by Multics
Honeywell, Inc., MULTICS records, 1965–1982
Charles Babbage Institute, University of Minnesota. Multics development records include the second MULTICS System Programmers Manual; MULTICS Technical Bulletins that describe procedures, applications, and problems, especially concerning security; and returned "Request for Comments Forms" that include technical papers and thesis proposals.
Official source code archive at MIT
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Active project to emulate the Honeywell dps-8/m Multics CPU

Various scanned Multics manuals


a critical review of Multicians.org, plus a capsule history of Multics. {{Authority control Multics, 1969 software AT&T computers Bell Labs Discontinued operating systems Free software operating systems General Electric mainframe computers Honeywell mainframe computers Massachusetts Institute of Technology software Time-sharing operating systems Mainframe computer software