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Multics ("Multiplexed Information and Computing Service") is an influential early
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence a ...
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
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. Nathan Gregory writes 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, United States. As part of the Boston metropolitan area, the cities population of the 2020 U.S. census was 118,403, making it the fourth most populous city in the state, behind Boston, ...
. Originally it was a cooperative project led by
MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
(
Project MAC Computer Science and Artificial Intelligence Laboratory (CSAIL) is a research institute at the Massachusetts Institute of Technology (MIT) formed by the 2003 merger of the Laboratory for Computer Science (LCS) and the Artificial Intelligence Lab ...
with
Fernando Corbató Fernando is a Spanish and Portuguese given name and a surname common in Spain, Portugal, Italy, France, Switzerland, former Spanish or Portuguese colonies in Latin America, Africa, the Philippines, India, and Sri Lanka. It is equivalent to the G ...
) along with
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
and
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
. It was developed on the
GE 645 The GE 645 mainframe computer was a development of the GE 635 for use in the Multics project. This was the first computer that implemented a configurable hardware protected memory system. The original CTSS was implemented on a modified IBM 7094 wi ...
computer, which was specially designed for it; the first one was delivered to MIT in January 1967. GE offered their earlier 635 systems with an early timesharing system known as "Mark I" and intended to offer the 645 with Multics as a larger successor. Bell withdrew from the project in 1969 as it became clear it would not deliver a working system in the short term. Shortly thereafter, GE decided to exit the computer industry entirely and sold the division to
Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...
in 1970. Honeywell offered Multics commercially, but with limited success. 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 telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
and
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
utilities A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and r ...
. 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, an access-control list (ACL) is a list of permissions associated with a system resource (object). An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on giv ...
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. Due to its many novel and valuable ideas, Multics has had a significant influence on
computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
despite its faults. Its most lasting effect on the computer industry was to inspire the creation of
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
, which was developed at Bell to allow their Multics team to continue their research using smaller machines, first a
PDP-7 The PDP-7 was a minicomputer produced by Digital Equipment Corporation as part of the PDP series. Introduced in 1964, shipped since 1965, it was the first to use their Flip-Chip technology. With a cost of , it was cheap but powerful by the s ...
and ultimately the PDP-11.


Novel ideas

Multics implements a
single-level store Single-level storage (SLS) or single-level memory is a computer storage term which has had two meanings. The two meanings are related in that in both, pages of memory may be in primary storage (RAM) or in secondary storage (disk), and that the ph ...
for data access, discarding the clear distinction between
file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...
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, activities that produce a specific se ...
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
''. The memory of a process consists solely of segments that were mapped into its address space. 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 circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
(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), a geometric shape * Disk storage Music * Disc (band), an American experimental music band * ''Disk'' (album), a 1995 EP by Moby Other uses * Disk (functional analysis), a subset of a vector sp ...
. In
POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...
terminology, it is as if every file were
mmap In computing, mmap(2) is a POSIX-compliant Unix system call that maps files or devices into memory. It is a method of memory-mapped file I/O. It implements demand paging because file contents are not immediately read from disk and initially use no ...
()
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 computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
has. ''All'' memory in the system is part of ''some'' segment, which appears in the
file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
; this includes the temporary scratch memory of the process, its kernel stack, etc. Segments are limited to 256
kiloword In computing, a word is the natural unit of data used by a particular processor design. A word is a fixed-sized datum handled as a unit by the instruction set or the hardware of the processor. The number of bits or digits in a word (the ''word s ...
s, just over 1  MB, because Multics hardware had 18-bit word addresses for the content of a segment. Larger files are "multisegment files" and are handled differently. The 256kW limit was rarely encountered in practice, because at the time, one megabyte of memory was prohibitively expensive. Another major new idea of Multics was
dynamic linking In computing, a dynamic linker is the part of an operating system that loads and links the shared libraries needed by an executable when it is executed (at " run time"), by copying the content of libraries from persistent storage to RAM, filling ...
, in which a running process can make external routines available by adding the segments containing them to its address space. This allows applications to always use the latest version of any external routine, since those routines are kept in other segments, which are dynamically linked only when a process first attempts to begin execution in them. Since different processes can use different search rules, different users can end up using different versions of external routines. Equally importantly, with the appropriate settings in the Multics security facilities, the code in the other segment can gain access to data structures maintained in a different process. Dynamic linking in Multics does not require special Dynamic-link libraries (DLLs); a program can dynamically link to any executable segment to which it has access rights. Thus, to interact with an application running in part as a
daemon Daimon or Daemon (Ancient Greek: , "god", "godlike", "power", "fate") originally referred to a lesser deity or guiding spirit such as the daimons of ancient Greek religion and Greek mythology, mythology and of later Hellenistic religion and Hell ...
(in another process), a user's process simply performs 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 can then modify data maintained and used in the daemon. When the action necessary to commence the request is completed, a simple procedure return instruction returns control of the user's process to the user's code. Multics also supports 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 circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...
s, memory banks, disk drives, etc. can be added and removed while the system continues 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 (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...
system into two separate systems during off-hours by incrementally removing enough components to form a second working system, leaving the rest still running for 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 supports multiple CPUs; it is one of the earliest multiprocessor systems. Multics is the first major operating system to be designed as a secure system from the outset. Despite this, early versions of Multics were compromised repeatedly. This led to further work that makes the system more secure, and prefigured modern security engineering techniques. Break-ins became very rare once the second-generation hardware base was adopted; it has 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 is the first operating system to provide a
hierarchical file system Hierarchical File System (HFS) is a proprietary file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. HFS i ...
, and file names can be of almost arbitrary length and syntax. A given file or directory can have multiple names (typically a long and short form), and symbolic links between directories are also supported. Multics is 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, activities that produce a specific se ...
stacks 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 learn ...
, with a separate stack for each security ring. It is also the first to have a
command processor A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
implemented as ordinary user code – an idea later used in the
Unix shell A Unix shell is a command-line Interpreter (computing), interpreter or shell (computing), shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting langua ...
. It is 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 computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...
),R. A. Freiburghouse
"The Multics PL/1 Compiler"
General Electric Company, Cambridge, Massachusetts, 1969.
after the Burroughs MCP system written in ESPOL, an expanded version of
ALGOL ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...
. 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
PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...
. Instead of being based on
phonemes In phonology and linguistics, a phoneme () is a unit of sound that can distinguish one word from another in a particular language. For example, in most dialects of English, with the notable exception of the West Midlands and the north-west o ...
, 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 645 mainframe computer was a development of the GE 635 for use in the Multics project. This was the first computer that implemented a configurable hardware protected memory system. The original CTSS was implemented on a modified IBM 7094 wi ...
mainframe, a
36-bit 36-bit computers were popular in the early mainframe computer era from the 1950s through the early 1970s. Starting in the 1960s, but especially the 1970s, the introduction of 7-bit ASCII and 8-bit EBCDIC led to the move to machines using 8-bit ...
system. GE's computer business, including Multics, was taken over by Honeywell in 1970; around 1973, Multics is supported on the
Honeywell 6180 The Honeywell 6000 series computers were rebadged versions of General Electric's 600-series mainframes manufactured by Honeywell International, Inc. from 1970 to 1989. Honeywell acquired the line when it purchased GE's computer division in 197 ...
machines, which included security improvements including hardware support for
protection ring In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security). Computer ...
s.
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
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 computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
system. Multics development continued at MIT and General Electric. At MIT in 1975, use of Multics was declining and did not recover by 1976 to prior levels. Finally by slashing prices, MIT managed to lure users back to Multics in 1978. 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 Trusted Computer System Evaluation Criteria (TCSEC) is a United States Government Department of Defense (DoD) standard that sets basic requirements for assessing the effectiveness of computer security controls built into a computer system. The ...
from the
National Computer Security Center The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collectio ...
(NCSC) a division of the
NSA The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collecti ...
, 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 company headquartered in Les Clayes-sous-Bois, in the western suburbs of Paris. The company has also been known at various times as Bull General El ...
in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, 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, no ...
license. The last known Multics installation running natively on Honeywell hardware was shut down on October 30, 2000, at the Canadian Department of National Defence 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, no ...
with the exception of some optional pieces such as
TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
. In 2014, Multics was successfully run on current hardware using an emulator. The 1.0 release of the emulator is 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 interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
. * apl *
ceil In mathematics and computer science, the floor function is the function that takes as input a real number , and gives as output the greatest integer less than or equal to , denoted or . Similarly, the ceiling function maps to the least int ...
* change_wdir (cwd) *
cobol COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily us ...
*
copy Copy may refer to: *Copying or the product of copying (including the plural "copies"); the duplication of information or an artifact **Cut, copy and paste, a method of reproducing text or other data in computing **File copying **Photocopying, a pr ...
(cp) *
echo In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the lis ...
* emacs * floor * fortran (ft) * gcos (gc) *
help Help is a word meaning to give aid or signal distress. Help may refer to: Arts, entertainment, and media Films * ''Help'' (2010 film), a Bollywood horror film * ''Help'' (2021 theatrical film), a British psychological thriller film * '' ...
*
home_dir A home, or domicile, is a space used as a permanent or semi-permanent residence for one or many humans, and sometimes various companion animals. It is a fully or semi sheltered space and can have both interior and exterior aspects to it. H ...
(hd) * if *
list A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations * List College, an undergraduate division of the Jewish Theological Seminary of America * SC Germania List, German rugby union ...
(ls) *
login In computer security, logging in (or logging on, signing in, or signing on) is the process by which an individual gains access to a computer system by identifying and authenticating themselves. The user credentials are typically some fo ...
(l) *
logout In computer security, logging in (or logging on, signing in, or signing on) is the process by which an individual gains access to a computer system by identifying and authenticating themselves. The user credentials are typically some form ...
* ltrim *
mail The mail or post is a system for physically transporting postcards, letter (message), letters, and parcel (package), parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid ...
(ml) * pascal * pl1 * print (pr) *
print_wdir Printing is the process for reproducing text and images using a master form or template Print or printing may also refer to: Publishing * Canvas print, the result of an image printed onto canvas which is often stretched, or gallery-wrapped, on ...
(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 that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock marke ...
(rf) * rtrim *
sort Sort may refer to: * Sorting, any process of arranging items in sequence or in sets ** Sorting algorithm, any algorithm for arranging elements in lists ** Sort (Unix), a Unix utility which sorts the lines of a file ** Sort (C++), a function in the ...
* 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), a serie ...
(wh) *
who Who or WHO may refer to: * Who (pronoun), an interrogative or relative pronoun * Who?, one of the Five Ws in journalism * World Health Organization Arts and entertainment Fictional characters * Who, a creature in the Dr. Seuss book '' Horton He ...
* working_dir (wd)


Retrospective observations

Peter H. Salus Peter Henry Salus is a linguist, computer scientist, historian of technology, author in many fields, and an editor of books and journals. He has conducted research in germanistics, language acquisition, and computer languages. Education and c ...
, 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, is said to have been 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 135 KB of code. The first
MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
GE-645 The GE 645 mainframe computer was a development of the GE 635 for use in the Multics project. This was the first computer that implemented a configurable hardware protected memory system. The original CTSS was implemented on a modified IBM 7094 wi ...
had 512 kilowords of memory (2 MiB), a truly enormous amount at the time, and the kernel used a moderate portion of Multics main memory. The entire system, including the operating system and the complex
PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
, user commands, and subroutine libraries, consists of about 1500 source modules. These average roughly 200 lines of source code each, and compile to a total of roughly 4.5 MiB of procedure code, which was fairly large by the standards of the day. Multics compilers generally optimise 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 is a good optimisation choice for Multics as a
multi-user Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving t ...
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 DPS 6 running 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 slightly influenced the
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
operating system, which was originally written by two Multics programmers,
Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
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 is 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 '' uniplexed'' as opposed to the ''
multiplex Multiplex may refer to: * Multiplex (automobile), a former American car make * Multiplex (comics), a DC comic book supervillain * Multiplex (company), a global contracting and development company * Multiplex (assay), a biological assay which measu ...
ed'' 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 A eunuch ( ) is a male who has been castrated. Throughout history, castration often served a specific social function. The earliest records for intentional castration to produce eunuchs are from the Sumerian city of Lagash in the 2nd millennium ...
" – 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 assachusetts Institute of Technologystill 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". Dennis Ritchie wrote that the design of UNIX was influenced by CTSS


Other operating systems

The
Prime Computer Prime Computer, Inc. was a Natick, Massachusetts-based producer of minicomputers from 1972 until 1992. With the advent of PCs and the decline of the minicomputer industry, Prime was forced out of the market in the early 1990s, and by the end of ...
operating system,
PRIMOS PRIMOS is a discontinued operating system developed during the 1970s by Prime Computer for its minicomputer systems. It rapidly gained popularity and by the mid-1980s was a serious contender as a mainline minicomputer operating system. With ...
, was referred to as "Multics in a shoebox" by William Poduska, a founder of the company. Poduska later moved on to found
Apollo Computer Apollo Computer Inc., founded in 1980 in Chelmsford, Massachusetts, by William Poduska (a founder of Prime Computer) and others, developed and produced Apollo/Domain workstations in the 1980s. Along with Symbolics and Sun Microsystems, Apollo ...
, whose AEGIS and later
Domain/OS Domain/OS is the discontinued operating system used by the Apollo/Domain line of workstations manufactured by Apollo Computer. It was originally launched in 1981 as AEGIS, and was rebranded to Domain/OS in 1988 when Unix environments were added to ...
operating systems, sometimes called "Multics in a matchbox", extends the Multics design to a networked graphics workstation environment. The
Stratus VOS Stratus VOS (Virtual Operating System) is a proprietary operating system running on Stratus Technologies fault-tolerant computer systems. VOS is available on Stratus's ftServer and Continuum platforms. VOS customers use it to support high-volume ...
operating system of Stratus Computer (now Stratus Technologies) is 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 are extended in Stratus VOS to support a new line of
fault tolerant Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
computer systems supporting secure, reliable
transaction processing Transaction processing is information processing in computer science that is divided into individual, indivisible operations called ''transactions''. Each transaction must succeed or fail as a complete unit; it can never be only partially comple ...
. 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 ICL's VME operating system. The
Edinburgh Multiple Access System The Edinburgh Multi-Access System (EMAS) was a mainframe computer operating system at the University of Edinburgh. The system went online in 1971. EMAS was a powerful and efficient general purpose multi-user system which coped with many of t ...
(EMAS) draws particularly on the one-level store concept used by Multics, providing access to files only by mapping them into memory. All memory space is associated with a segment.


See also

*
Time-sharing system evolution This article covers the evolution of time-sharing systems, providing links to major early time-sharing operating systems, showing their subsequent evolution. Time-sharing Time-sharing was first proposed in the mid- to late-1950s and first impleme ...
* Peter J. Denning *
Jack B. Dennis Jack Bonnell Dennis (born October 13, 1931) is a computer scientist and Emeritus Professor of Computer Science and Engineering at Massachusetts Institute of Technology. The work of Dennis in computer systems and computer languages is recogniz ...
*
Robert Fano Roberto Mario "Robert" Fano (11 November 1917 – 13 July 2016) was an Italian-American computer scientist and professor of electrical engineering and computer science at the Massachusetts Institute of Technology. He became a student and working ...
– director of Project MAC at MIT (1963–1968) * Robert M. Graham (computer scientist) *
J. C. R. Licklider Joseph Carl Robnett Licklider (; March 11, 1915 – June 26, 1990), known simply as J. C. R. or "Lick", was an American psychologistMiller, G. A. (1991), "J. C. R. Licklider, psychologist", ''Journal of the Acoustical Society of Am ...
– director of Project MAC at MIT (1968–1971) *
Peter G. Neumann Peter Gabriel Neumann (born 1932) is a computer-science researcher who worked on the Multics operating system in the 1960s. He edits the RISKS Digest columns for ACM ''Software Engineering Notes'' and ''Communications of the ACM''. He founded ...
*
Elliott Organick Elliott Irving Organick (February 25, 1925 – December 21, 1985) was a computer scientist and pioneer in operating systems development and education. He was considered "the foremost expositor writer of computer science", and was instrumental in f ...
*
Louis Pouzin Louis Pouzin (April 20, 1931 in Chantenay-Saint-Imbert, Nièvre, France) is a French computer scientist. He designed an early packet communications network, CYCLADES. This network was the first actual implementation of the pure datagram model, ...
– introduced the term ''shell'' for the command language used in Multics * Jerome H. Saltzer * Roger R. Schell *
Glenda Schroeder Glenda Schroeder is an American software engineer noted for implementing the first command-line user interface shell and publishing one of the earliest research papers describing electronic mail systems while working as a member of the staff at th ...
– implemented the first
command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
and proposed the first
email Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" meant ...
system with Pouzin and Crisman *
Victor A. Vyssotsky Victor Alexander Vyssotsky (russian: Виктор Александрович Высотский; February 26, 1931 - December 24, 2012 in Orleans, Massachusetts) son of the astronomers Alexander N. Vyssotsky (Russian) and Emma Vyssotsky ( Americ ...


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. * F. J. Corbató, V. A. Vyssotsky
''Introduction and Overview of the Multics System''
(
AFIPS The American Federation of Information Processing Societies (AFIPS) was an umbrella organization of professional societies established on May 10, 1961, and dissolved in 1990. Its mission was to advance knowledge in the field of information science, ...
1965) is a good introduction to the system. * 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, 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 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. * V. A. Vyssotsky, 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, 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, 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,

', ( ACM SOSP, 1969) describes the Multics memory system in some detail. * 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 D. Schroeder,
The Protection of Information in Computer Systems
' (Proceedings of the
IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
, September 1975) describes the fundamentals behind the first round of security upgrades; another classic paper. * 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 *

*

*

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 *

*

*

Includes extensive overview of other software systems influenced by Multics
Open source emulator for the GE Large Systems / Honeywell / Bull 600/6000‑series mainframe computers

Honeywell, Inc., MULTICS records, 1965–1982
Charles Babbage Institute The IT History Society (ITHS) is an organization that supports the history and scholarship of information technology by encouraging, fostering, and facilitating archival and historical research. Formerly known as the Charles Babbage Foundation, ...
, 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.
Current Multics development home page

Official historical source code archive at MIT
*




Various scanned Multics manuals


a critical review of Multicians.org, plus a capsule history of Multics. {{Authority control 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