Multics - Wikipedia
Some of the links to external sites covering other operating systems Multics was coherent and rational, where UNIX is chaotic and whimsical. Multics is an influential early time-sharing operating system, based around .. [ edit]. guiadeayuntamientos.info is a comprehensive site with a lot of material Multics security · Unix and Multics · Multics general info and FAQ. Multics was the first or one of the first operating systems that used (pronounced MUHL-tihx) inspired the creators of a newer operating system to call it Unix.
Sam Morgan, director of Computing Science Research at Bell Labs during this period, expressed his own concerns that Multics research was going very slowly and wasting effort, saying: The development was moving more slowly than had been expected and users were sighing with varying degrees of pungency.
It became clear that we were a drag on the computer center's budget.
Although Bell Labs had dropped out of the Multics project in Aprilthose of us in Cambridge kept in touch with individual folks at BTL, and so we knew that Ken and Dennis were working on a project of their own. We even knew that it had a joke name, Unix, coined by Brian Kernighan, that was a reference to Multics. The second of these conferences was held in Elmsford, NY inand Ken and Dennis gave a talk there, presenting Unix.
Several of us Multicians went to the conference, and sat with the Bell Labs ex-Multicians and applauded the paper, which was and remains one of the best and clearest pieces of writing in the computer field. There were some other great papers at that conference, but as I remember, the Unix paper won the best paper award.
The idea of a free, non-vendor-supported operating system was new to them. I invited Dennis Ritchie to come up and talk to them. We went to lunch afterward, and I remarked to Dennis that easily half the code I was writing in Multics was error recovery code. Together with the C programming language, developed as part of the same project, the slightly renamed UNIX became the leading research operating system of s.
Inshortly after Bell Labs dropped out of the project, General Electric abandoned its computer hardware business without ever having used Multics. Honeywell acquired GE's computer division, and with it the Multics effort. Honeywell boasted several other operating systems, each supported by its own internal groups. Although around 80 Multics sites were installed between its debut as a standard commercial product in and its cancellation inthe operating system never attained critical mass in the marketplace, or even won clear internal acceptance as Honeywell's own next-generation product.
MIT continued to collaborate in its development untilafter which point the burden passed exclusively to Honeywell, which in turn divested its computer operations to the French firm Bull. The last Multics site was closed down in The initial target market of commercial "computer utilities" never fully developed, due in part to unexpected difficulty in producing efficient operating systems on this scale and in part to the equally unanticipated emergence of powerful minicomputers as a cost-effective alternative.
Unix and Multics
Its two largest groups of users were universities, for whom the ability to support diverse types of users simultaneously was an attraction, and governmental research centers in the USA, Canada, and France.
While many Multics installations enjoyed long and productive lives, its primary achievement was as a research project rather than a working operating system. No emulator has been produced for any of the machines it ran on, and the source code is still guarded by Bull.
The site functions primarily as the hub of an otherwise destroyed community of developers, managers, application programmers and users involved with the system over its three and a half decade career. Its creators believe that "as long as we have the Multicians, we have the most important part of Multics.AT&T Archives: The UNIX Operating System
A few dozen of these people have contributed actively to the development of the Multicians site and its precursors. Its main contents are lists of and links to original technical papers and development documents, a glossary of Multics terms, personal home pages and individual reminiscences.
The reminiscences include accounts of Multics operations at particular user sites, and the memories of some of the original system designers.
Much of the site's content was originally assembled from the FAQs of the long-established Usenet newsgroup alt. This makes for something of a patchwork impression. Some five year old articles still include placeholders reminding the author to check certain information or fill in a particular section. Some installations and aspects of the Multics development story receive elaborate treatment, while others are ignored completely. Indeed, the site lacks a simple overall description of Multics and its significance.
Unix and Multics
Many documents assume a detailed knowledge of Multics hardware and terminology, or of operating system concepts. For example, the use of Multics as a commercial product and the relationship of Multics to the "computer utility" concept are both referenced repeatedly but neither receives a clear overall statement.
Some of the links to external sites covering other operating systems of interest are broken, or point to sites with little relevant content.
Many of these links are useful, though neither here nor elsewhere are any published works by historians of computing referenced. This reflects the general focus of the site on technical aspects of the story, and toward Multics participants and younger software engineers. Its editors have made some efforts to bring structure to the site.
It can be browsed via a chronology of events, an alphabetical list of Multics installations supplemented by a chart showing the years during which each was in operationa somewhat sketchy attempt at an overall history, and a list of online documents.
It represents an intriguing mixture of archive, public relations on behalf of a defunct product, and private conversation between long-time colleagues. Its intended relationship to a wider audience is not entirely clear.
CSa: UNIX and Multics
The site itself lists its purposes as preserve the technical ideas and advances of the system so others don't need to reinvent them.
Notable in their absence from this list are needs of professional historians and the general public. It can be assumed that they have been taken care of. The first, preservation of good ideas, is an important one. To read or write to them, the process simply used normal central processing unit 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 were 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. This was due to the particular hardware architecture of the machines on which Multics ran, having a bit 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 graphics, this limit was rarely encountered. Another major new idea of Multics was dynamic linkingin 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 rulesdifferent 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 in another processa 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. The single-level store and dynamic linking are still not available to their full power in other widely used operating systems, despite the rapid and enormous advance in the computer field since the s.
They are becoming more widely accepted and available in more limited forms, for example, dynamic linking. Multics also supported extremely aggressive on-line reconfiguration: At the MIT system, where most early software development was done, it was common practice to split the multiprocessor 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.