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Bibliography | 10 Sites | 11 Chronology 12 Stories | 13 Glossary | 14 Papers | 15 Humor | 16 Documents | 17 Source | 18 Links | 19 Site Map | 20 About Contents 21 1. Summary Multics (Multiplexed Information and Computing Service) is a timesharing operating system begun in 1965 and used until 2000. The system was started as a joint project by 36 MIT's 37 Project MAC, 38 Bell Telephone Laboratories, and 39 General Electric Company's Large Computer Products Division. Bell Labs withdrew from the development effort in 1969, and in 1970 GE sold its computer business to 41 Honeywell, which offered Multics as a commercial product and sold a few dozen systems. Multics was introduced in a series of papers at the 1965 Fall Joint Computer Conference: * " 42 Introduction and Overview of the Multics System," F. Vyssotsky * " 44 System Design of a Computer for Time-Sharing Applications," 45 E. Graham * " 50 A General Purpose File System for Secondary Storage," 51 R. Dunten * " 57 Some Thoughts About the Social Implications of Accessible Computing," 58 E. Fano 60 Many books and papers describe aspects of the system. The influence of Multics on Unix is described in chapter 3 of A Quarter Century of UNIX, for example. Multics runs on special expensive CPU hardware that provides a 61 segmented, 62 paged, 63 ring-structured 64 virtual memory. The system is a symmetric 65 multiprocessor with shared physical and virtual memory. MIT started providing timesharing service on Multics to users in fall of 1969. GE sold the next system to the 69 US Air Force, and the military use of Multics led to some of the system's security features. Honeywell sold more systems to government, and to auto makers, universities, and commercial data processing services. Honeywell's partner 70 Bull sold a total of 31 Multics sites. Honeywell decided not to create a new hardware generation for Multics in the mid-80s and stopped developing the operating system. Subsequently, Honeywell sold its computer business to Bull, which also chose not to build new Multics hardware, and all sites replaced their Multics systems with more modern hardware. Goals As described in the 1965 paper 71 Introduction and Overview of the Multics System by Corbat and Vyssotsky, there were nine major goals for Multics: * Convenient remote terminal use. Notable features See the 74 Multics Features FAQ for more information. Segmented memory The Multics memory architecture divides memory into 75 segments. The 76 file system is integrated with the memory access system so that programs access files by making memory references. Virtual memory Multics uses paged memory in the manner pioneered by the Atlas system. Addresses generated by the CPU are translated by hardware from a virtual address to a real address. A hierarchical three-level scheme, using main storage, 77 paging device, and disk, provides transparent access to the virtual memory. High-level language implementation Multics was written in the 78 PL/I language, which was, in 1965, a new proposal by IBM. Only a small part of the operating system was implemented in assembly language. Writing an OS in a high-level language was a radical idea at the time. Shared memory multiprocessor The Multics hardware architecture supports multiple CPUs sharing the same physical memory. Multi-language support In addition to PL/I, Multics supports BCPL, BASIC, APL, FORTRAN, LISP, C, COBOL, ALGOL 68 and Pascal. Relational database Multics provided the first commercial relational database product, the 79 Multics Relational Data Store (MRDS), in 1978. Security Multics was designed to be secure from the beginning. In the 1980s, the system was awarded the 80 B2 security rating by the US government 81 NCSC, the first (and for years only) system to get a B2 rating. On-line reconfiguration As part of the computer utility orientation, Multics was designed to be able to run 7 days a week, 24 hours a day. CPUs, memory, I/O controllers, and disk drives can be added to and removed from the system configuration while the system is running. Software Engineering The development team spent a lot of effort finding ways to build the system in a 82 disciplined way. The Multics System Programmer's Manual ( 83 MSPM) was written before implementation started: it was 3000 or so pages and filled about 4 feet of shelf space in looseleaf binders. Unix 85 Ken Thompson and 86 Dennis Ritchie, the inventors of 87 Unix, worked on Multics until Bell Labs dropped out of the Multics development effort in 1969. The Unix system's name is a pun on Multics attributed to 88 Brian Kernighan. Some ideas in Multics were developed further in 89 Unix. GCOS 6 Honeywell's GCOS 6 operating system for the 90 Level 6 minicomputers was strongly influenced by Multics. Primos 91 Prime's Primos operating system shows a strong Multics influence. VOS Stratus's VOS operating system shows a strong Multics influence. For instance, the basic access to stuff on disk is via a single-level store directly based on Multics. Supposedly some of the motivation for the object-store style of file system came from Multics too. NTT DIPS 96 Carl Hoffman NTT undertook a massive effort to clone Multics, which led to their DIPS (Denden Information Processing System) series of mainframes. DIPS machines are still in widespread use in Japan today by NTT, but everyone agrees that they are going away. I believe that Intermetrics developed the DIPS PL/I compiler for NTT. Sure, it was inspired by Multics, but was not a clone, or you would call every multi-user machine built after 1970 a Multics clone. Amber Multics also influenced 98 Amber, the operating system produced by the S-1 project at Livermore between 1979 and 1986 or so. The original Amber group was familiar with Multics as users - the original development work was done on MIT-Multics - but I don't believe it included anyone who'd actually worked on the Multics kernel itself. The most important Multics influences were writing the operating system in a high-level language, the single-level storage system, and an emphasis on security, although rings were not present on the last generation of S-1 machine. Amber was heavily influenced by critiques of Multics such as the Multics Kernel Redesign Project. In its later years, Amber made serious strides toward machine independence. GEMSOS 101 Paul Karger The Gemini GEMSOS secure operating system for the Intel architecture was developed by 102 Roger Schell to support a Multics-style segmented environment in a system designed to meet A1 security requirements. IBM systems As for other systems influenced, TSS/360 was strongly influenced by Multics. And IBM's MVS eventually acquired dynamic reconfiguration to add processors and memory without shutting down. Jerry Saltzer The IBM System/38 maps files into the one-level store just like Multics, and so does AIX, down underneath where it is hard to find because it is trying to pretend it is a Unix. Both of these systems are derivatives of IBM FS, which never saw the light of day, but which borrowed the file mapping/one-level-store idea from TSS/360, which in turn got it from Multics. TENEX and TOPS-20 Multics influenced the paging design of TENEX and the DECSYSTEM-20, and several Multicians provided review and comment on the TENEX design. Dan Murphy has written a fine paper on the history of 103 TENEX and TOPS-20, available online. In this paper he says: Multics may be said to have contributed more than just the ideas for virtual memory organization and other specific capabilities. During the design of TENEX, we invited some of the Multics designers and implementors to review our progress and decisions. As is often the case, we had fallen into the trap of trying to do too much in a number of areas and had produced some designs that were quite convoluted and complex. Several people from Multics beat us up on those occasions, saying "this is too complicated -- simplify it! Murphy has also posted the classic 1972 paper on 104 TENEX by Bobrow, Burchfiel, Murphy, and Tomlinson. Michigan Terminal System MIT Comp Center and University of Michigan had close ties in the early 60s, and there was an informal group studying vi...
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