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The end of Multics

By Maniac in Technology
Mon Nov 13, 2000 at 02:59:17 PM EST
Tags: Technology (all tags)
Technology

I heard about the end of Multics in the following Risks Digest article. This system lasted for 35 years and was a predecessor to Unix. In many ways, Multics was the best system I've ever used and would like to see some commentary about it and other systems that made an impact to you.


For those who haven't used Multics, there is more information at the Multics Home. A brief summary about what I liked and disliked about that system follows.
  • Paged and segmented memory. There are lots of pros and cons to segmented memory but this is what made Multics capable of doing a number of other things.
  • Dynamic linking. When you compiled files separately, the result was a set of "object files". There was no "linker" - the same search path for command execution was used to find the objects needed to run your program. Forget to compile one - you'd get a new shell when the lookup failed, compile it, resume and the program kept on running! Excellent for a development machine.
  • I/O redirection based on procedure calls. The ioa_ function provided a list of common operations on any I/O stream - read, write, control, read direct, read indexed, etc. Behind the scenes was a structure with pointers to compatible procedure calls for that operation. It was EASY to write code compatible with this and a variety of filters were available. One of my favorites was the Tektronix graphics filter which added graphics input, and graphics output to the basic set of standard input, standard output, and error output. On other systems, any "system messages" put garbage on your display. On Multics, they came out at the bottom of the screen and graphics were not disturbed. There were also filters for command history, editing, etc. Every program could take advantage of them.
  • Rings. Organick's book on Multics described rings in detail. We (users, not system administrators) used rings 4 and 5 to implement a secure software CM system.
  • Reliable operation. Designed and operated to be as reliable as facility power.
  • Ted. One of the first scriptable editors - basic syntax similar to ed on Unix but supported multiple buffers, execute a buffer, etc. I made many tools with ted.
  • Intelligent use of dates. Each file had 5 date/times recorded - created, last accessed, modified, contents backed up, entry backed up. The entry is similar to a Unix inode. Backups would store the content or entry as needed.
  • 8 bit support (actually 9 bit - a 36 bit machine) for text.
  • Supported networks. HI-MULTICS.ARPA.COM was on the ARPANet relatively early. DOCKMASTER was on the Internet until it was shut down a few years ago. We also had good links to smaller systems across the country with dedicated lines as well.
  • Discuss. A great bulletin board system for exchanging and managing information.
  • Lrk. By David Ward - a much better program than yacc for generating compilers. Bison is getting better but still lacks in some areas. Excellent error recovery for generated compilers - four local and a more global error recovery implemented for ALL parsers.
  • Hierarchical file system. Seen on most if not all systems today. Multics had it in the 60's.
  • Resource allocation. Linux is starting to get bean counters. Multics had it in '76.
  • Upgradable. Read the story about the last machine. It had DAT's installed 16 years after first use!
Overall, Multics was a great system. I am certain other people have similar stories. I have far more capability in CPU and memory at my desk as I compose this, but the tools on Multics were in many ways better then than now. Is there some way we can capture the "best of" from that system and those others and move it into these newer ones?

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Related Links
o Risks Digest article
o Multics Home
o story
o Also by Maniac


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