TECHWARZ

(Multiplexed Information and Computing Service)  Multics was an extremely influential early time-sharing operating system.  Goal: Develop a convenient, interactive, useable time shared computer system that could support many users.  The project was started in  The normal mode of operation on Multics is interactive, or "conversational": each instruction that you type goes directly to the computer and is acted on immediately.  The last known running Multics installation was shut down on October 30, 2000 at the Canadian Department of National Defence in Halifax, Nova Scotia, Canada.

LOOGGING IN:  Entering the Multics system is called logging in.  When you have successfully connected your terminal, Multics prints a banner, or greeting message.  This is the signal for you to log in and identify yourself. LOOGGING OUT:  Leaving the system is called logging out.  When you finish your work on Multics, wait for a ready message and type the logout command to break your terminal connection.  Multics responds by printing your User_id, the date and time that you log out, and your total system resource usage.

 Multics is conveyed by commands.  There are over 400 commands.  Most commands share several established rules of usage called conventions.  Command names are always typed in lowercase letters.  Command names never contain blanks.

 Multics offers several commands that allow you to communicate with other users.  This facility - known as the mail facility.  The mail facility commands are described below in two groups: message commands and mail commands.  Message commands provide the advantage of: - Receiving messages. - Sending messages.  Mail commands provide the advantage of: - Reading mail. - Sending mail.

Text Editing.  After logging in and becoming familiar with the basic Multics environment, you will probably want to create and edit information on Multics.  Multics has several text editors, powerful interactive commands that enable you to create, edit, and store your own segments.  The two primary text editors on Multics are commands named qedx and emacs.  There are two modes of operation in qedx: Input mode: For entering new text. Edit mode: You make changes to already existing text.

 There are many commands on Multics that enable you to work with both your own segments and those of other users.  There are several commands that help us to manipulate segments. 1. Viewing Segments. - The print Command. - The dprint Command. 2. Naming Segments. 3. Segment Attributes. 4. Deleting Segments.

 A directory is a catalogue of the segments.  It contains information about all the attributes of each segment.  The segments and directories just described are part of the Multics storage system.  Every segment and directory in the system (except the root directory, the originating directory of the Multics system) is immediately under another directory. Imagine it this way: directory Segment 1 Segment 2 Segment 3

 One of the overall design goals is to create a computing system which is capable of meeting almost all of the present and near-future requirements of a large computer utility.  Such systems must run continuously and reliably 7 days a week, 24 hours a day in a way similar to telephone or power systems, and must be capable of meeting wide service demands: from multiple man machine interaction to the sequential processing of absentee-user jobs.  Such information processing and communication systems are believed to be essential for the future growth of computer use in business, in industry, in government and in scientific laboratories as well as stimulating applications which would be otherwise undone.

Segmented memory:  The Multics memory architecture divides memory into segments. Each segment has addresses from 0 to 256K words (1 MB).  The 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, paging device, and disk, provides transparent access to the virtual memory. High-level language implementation:  Multics was written in the 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.

Shared memory multiprocessor:  The Multics hardware architecture supports multiple CPUs sharing the same physical memory. All processors are equivalent. Multi-language support:  In addition to PL/I, Multics supports BCPL, BASIC, APL, FORTRAN, LISP, C, COBOL, ALGOL 68 and Pascal. Routines in these languages can call each other. Relational database:  Multics provided the first commercial relational database product, the Multics Relational Data Store (MRDS), in Security:  Multics was designed to be secure from the beginning.  In the 1980s, the system was awarded the B2 security rating by the US government NCSC, the first 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 disciplined way.  The Multics System Programmer‘s Manual (MSPM) was written before implementation started: it was 3000 or so pages and filled about 4 feet of shelf space in loose leaf binders.  High level language, design and code review, structured programming, modularization and layering were all employed extensively to manage the complexity of the system, which was one of the largest software development efforts of its day.