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Multics (Multiplexed Information and Computing Service) was an extraordinarily influential early time-sharing operating system. Alternate uses: see Timesharing Time-sharing is an approach to interactive computing in which a single computer is used to provide apparently simultaneous interactive general-purpose computing to multiple users by sharing processor time. ...
// An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ...
Overview Initial planning and development for Multics started in 1964. Originally it was a cooperative project led by MIT (with Fernando Corbató), along with General Electric and Bell Labs. Bell Labs dropped out in 1969, and in 1970 GE's computer business, including Multics, was taken over by Honeywell. 1964 (MCMLXIV) was a leap year starting on Wednesday (the link is to a full 1964 calendar). ...
The Massachusetts Institute of Technology (MIT) is a private, coeducational research university located in Cambridge, Massachusetts. ...
Fernando José Corbató (born July 1, 1926) is a prominent computer scientist, notable as a pioneer in the development of time-sharing operating systems. ...
This article is about the American company. ...
Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ...
For the Stargate SG-1 episode, see 1969 (Stargate SG-1). ...
1970 (MCMLXX) was a common year starting on Thursday. ...
Honeywell Heating Specialties Company Stock Certificate dated 1924 signed by Mark C. Honeywell - courtesy of Scripophily. ...
Multics was conceived as a commercial product for GE, and it did achieve that for Honeywell, although it was not a very successful one. However, it had a powerful impact in the computer field, due to its many novel and valuable ideas. Although it was much derided at the time by its critics [1], history has shown these complaints to be canards. In aeronautics, canard (French for duck) is a type of fixed-wing aircraft in which the tailplane is ahead of the main lifting surfaces, rather than behind them as in conventional aircraft, or when there is an additional small set of wings in front of the main lifting surface. ...
It had numerous features intended to result in high availability, so that it would produce a computing utility, similar to the telephone and electricity services. To achieve this, in addition to being modular in software structure, the hardware was too, and the system could grow in size by simply adding more of the appropriate resource - computing power, main memory, disk storage, etc. Separate Access Control Lists on every file provided flexible information sharing, but also provided complete privacy when needed. It contained 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. This article does not cite any references or sources. ...
This article or section includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ...
Lightning strikes during a night-time thunderstorm. ...
In computer security, an access control list (ACL) is a list of permissions attached to an object. ...
Novel ideas Multics was an early operating system that implemented a single level store for data access, discarding the clear distinction between files (called segments in Multics) and process memory. The memory of a process consisted solely of segments which were mapped into its address space; to read or write to them, the process simply used normal CPU instructions, and the operating system took care of making sure that all the modifications were saved to disk. In POSIX terminology, it was as if every file was mmap()ed; however, in Multics there was no concept of process memory, separate from the memory used to hold mapped in files, as Unix has. All memory in the system was part of some segment, which appeared in the file system; this included the temporary scratch memory of the process, its kernel stack, etc. ‹ The template below (Expand) is being considered for deletion. ...
A computer file is a collection of information that is stored in a computer system and can be identified by its full path name. ...
In computing, a process is, roughly speaking, a task being run by a computer, often simultaneously with many other tasks. ...
The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ...
The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...
Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ...
Disk storage is a group of data storage mechanisms for computers; data are transferred to planar surfaces or disks for temporary or permanent storage. ...
POSIX or Portable Operating System Interface[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system. ...
In computing, mmap() is a POSIX-compliant Unix system call that maps files or devices into memory. ...
It has been suggested that Crash counting be merged into this article or section. ...
One disadvantage of this in practice, due only to the particular hardware architecture of the particular machines it ran on, and not a result of the basic concept, was that the size of segments was limited to 256K 36-bit words, roughly equal to 1 megabyte by today's standards, and therefore extra code had to be used to work on files larger than this, called multi-segment files. In the days before large databases and, later, huge bitmap graphics, this limit was rarely encountered. For the use of the term raster in radio regulation, see frequency raster. ...
This led to the second of Multics' major new ideas, dynamic linking, 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. With this facility available, applications automatically used the latest version of any external routine they called, since those routines were kept in other segments, which were dynamically linked in only when a process first tried to begin execution in them. Since different processes, belonging to different users, 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. In computer science, a library is a collection of subprograms used to develop software. ...
Thus, to interact with an application running in part as a daemon (in another process), a user's process simply performed a normal procedure call instruction, to a code segment which it had dynamically linked to (a code segment which 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. In Unix and other computer multitasking operating systems, a daemon is a computer program that runs in the background, rather than under the direct control of a user; they are usually instantiated as processes. ...
It is worth noting that these two ideas, in their full power, are even now still not available in other widely used operating systems, despite the rapid and otherwise enormous advance in the computer field since the 1960s; although in more limited forms they are now becoming more widely accepted and available, e.g. dynamic linking. The 1960s decade refers to the years from January 1, 1960 to December 31, 1969, inclusive. ...
Multics also supported extremely aggressive on-line reconfiguration; CPUs, memory banks, disk drives, etc. could all be added and removed while the system continued operating; being added into service, or removed from it, as required. (In fact, it was common practice at the MIT system, where most early software development was done, to split the system — which was a multi-processor 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 performed on the second machine; when testing was over, the components of the second system would be added back onto the main user system, without ever having shut it down.) Since multiple CPUs were supported, it was thus one of the earliest multi-processor systems. Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ...
Multics was also notable for its early emphasis on computer security by design, and Multics was possibly the very first operating system to be designed as a secure system from the ground up. In spite of this, early versions of Multics were broken into, not once, but repeatedly. This led to further work on improved security that both prefigured modern security engineering techniques, and made the system much more secure; once the second-generation hardware base was adopted, with hardware support for ring-oriented security (a multi-level refinement of the concept of master mode), break-ins became very rare. This article describes how security can be achieved through design and engineering. ...
Security engineering is the field of engineering dealing with the security and integrity of real-world systems. ...
In computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults (fault tolerance) and malicious behaviour (computer security). ...
In processors with memory protection, kernel mode (as opposed to user mode) is the mode in which the operating system kernel runs. ...
In addition to having been the first operating system to provide a hierarchical file system, filenames 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. It was the first to use the now-standard concept of having per-process stacks in the kernel, with a separate stack for each security ring. It was also one of the first written in a high level language; PL/I was used, though the Burroughs B5000 system (1961), which used ALGOL, preceded Multics. In computing, a process is an instance of a computer program that is being executed. ...
Simple representation of a stack In computer science, a stack is a temporary abstract data type and data structure based on the principle of Last In First Out (LIFO). ...
In computer science, the kernel is the fundamental part of an operating system. ...
PL/I (Programming Language One, pronounced pee el one) is an imperative computer programming language designed for scientific, engineering, and business applications. ...
The Burroughs large systems were the largest of three series of Burroughs Corporation mainframe computers. ...
Algol (β Per / Beta Persei) is a bright star in the constellation Perseus. ...
Project history Multics was developed initially for the GE-645 mainframe, a 36-bit system; later, it was supported on the Honeywell 6180 series machines. The GE-600 series was a family mainframe computers of the 1960s, built by General Electric. ...
In 1970 General Electric sold their computing division to Honeywell. ...
Bell Labs pulled out of the project in 1969; some of the people who had worked on it there went on to create the Unix system. Superficially, UNIX shows the influence of Multics in many areas, down to the naming of commands. The design philosophy was quite different, however, focusing on keeping the system as small and as simple as possible, and thus correcting what was seen as the deficiencies of Multics. The name "Unix" (originally "Unics") is itself a hack on "Multics". The U in UNIX is rumoured to stand for "Uniplexed" as opposed to the "Multiplexed" of Multics, further underscoring the designers' rejections of Multics' complexity in favour of a more straightforward and workable approach. For the Stargate SG-1 episode, see 1969 (Stargate SG-1). ...
Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ...
A hack in progress in Lobby 7 at MIT. Hack is a term in the slang of the technology culture which has come into existence over the past few decades. ...
Honeywell bought G.E.'s computer division, released a better hardware base, and continued system development until 1985. About 80 multi-million-dollar sites were installed, at universities, industry, and government sites. The French university system had quite a few in the early 1980s. After Honeywell stopped supporting Multics, users migrated to other systems including the Unix system. Honeywell Heating Specialties Company Stock Certificate dated 1924 signed by Mark C. Honeywell - courtesy of Scripophily. ...
Year 1985 (MCMLXXXV) was a common year starting on Tuesday (link displays 1985 Gregorian calendar). ...
This article does not cite any references or sources. ...
The last Multics machine was shut down on October 31, 2000 at the Canadian Department of National Defence. is the 304th day of the year (305th in leap years) in the Gregorian calendar. ...
2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ...
Multics was distributed in 1975 to 2000 by Groupe Bull in Europe, and in the U.S. by Bull HN Information Systems Inc. In 2006 Bull SAS open sourced Multics versions MR10.2, MR11.0, MR12.0, MR12.1, MR12.2, MR12.3, MR12.4 & MR12.5.[2] Groupe Bull (also known as Bull Computer or, informally, as Bull) is a French computer company based in Paris. ...
Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ...
Retrospective observations It is more than a little startling to realize that the permanently resident kernel of this powerful multi-processor mainframe computing utility, much derided in its day as being too large and too complex, was a mere 135 Kbytes of code. The first MIT GE-645 had 512K words of memory (2 Mbytes), so the kernel only used a moderate portion of Multics main memory. A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to the decimal 1024 bytes (2 to the 10th power, or 1,024 bytes based in the binary system). ...
Mapúa Institute of Technology (MIT, MapúaTech or simply Mapúa) is a private, non-sectarian, Filipino tertiary institute located in Intramuros, Manila. ...
ReBoot character, see Megabyte (ReBoot). ...
Measured another way, the entire system, including not just the operating system, but also the complex PL/I compiler, user commands, and subroutine libraries, consisted of about 1500 total source modules. These averaged roughly 200 lines of source code each, and compiled to produce a total of roughly 4.5 Mbytes of procedure code, which though small today was fairly large by the standards of the day. It has been suggested that this article or section be merged with Compile (software company). ...
ReBoot character, see Megabyte (ReBoot). ...
Multics compilers generally optimised more for code density than CPU performance, for example using small sub-routines called operators for short standard code-sequences, making direct comparison of object code size with more modern systems less useful. High code density was a good optimisation choice for a multi-user system with expensive main memory, such as Multics.
See also Fernando José Corbató (born July 1, 1926) is a prominent computer scientist, notable as a pioneer in the development of time-sharing operating systems. ...
Jerome H. Saltzer (born October 9, 1939 Nampa, Idaho) is a computer scientist who has made many notable contributions. ...
Jack B. Dennis is an electrical engineer and a computer scientist. ...
Peter J. Denning is a computer scientist and one of the team members of the Multics project. ...
Robert M. Graham (born 1929 in Michigan) is a computer scientist. ...
Victor A. Vyssotsky (born ) son of Alexander N. Vyssotsky and Emma T. R. Williams is a mathematician and computer scientist. ...
Louis Pouzin, from France, inveted the datagram and designed the first packet communications network, CYCLADES. He also created the first forms of command-line interface. ...
Peter G. Neumann is a researcher who has worked on the Multics operating system. ...
Dr. Roger R. Schell is President of ÆSec, a company focused on appliances built on hardened platforms for secure, reliable e-business on the Internet. ...
Further reading The literature contains a large number of papers about Multics, and various components of it; a fairly complete list is available here. The most important and/or informative ones are listed below.
Further reading - 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, The Multics Virtual Memory: Concepts and Design, (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.
The Association for Computing Machinery, or ACM, was founded in 1947 as the worlds first scientific and educational computing society. ...
Further reading - 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, 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.
A tiger team is an individual, or more commonly a collection of individuals, who are employed or contracted by an organization to attempt to break its security, as a means of testing the reliability of that security. ...
The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ...
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