1/29 Early monolithic kernels: Multics and Unix

Reading

1. “Multics—The first seven years”, F. J. Corbató, J. H. Saltzer, and C. T. Clingen (1972 Spring Joint Computer Conference)

2. “Protection in an information processing utility”, Robert M, Graham (1968)

3. “The evolution of the Unix time-sharing system”, Dennis M. Ritchie (1979/1984—this version AT&T Bell Laboratories Technical Journal 63(6), October 1984)

Reading questions

1. How do Multics’s “insights” (paper #1) and protection mechanisms (paper #2) relate to its “goals” (paper #1)?
2. Which Multics “goals” did Unix give up on? Why?
3. Which Multics “goals” remain unachieved in modern operating systems?

Further reading

• The Multicians web site for additional information on Multics, including extensive stories and Multics source code.

  • Technical: The Multics input/output system, Feiertag RJ and Organick EI, for a description of Multics I/O to contrast with Unix I/O.

  • Unix and Multics, Tom Van Vleck.

    … I remarked to Dennis that easily half the code I was writing in Multics was error recovery code. He said, "We left all that stuff out. If there's an error, we have this routine called panic(), and when it is called, the machine crashes, and you holler down the hall, 'Hey, reboot it.'"

  • The Louisiana State Trooper Story

  • The IBM 7094 and CTSS

    This describes the history of the system that preceded Multics, CTSS (the Compatible Time Sharing System). It also contains one of my favorite stories about the early computing days: “IBM had been very generous to MIT in the fifties and sixties, donating or discounting its biggest scientific computers. When a new top of the line 36-bit scientific machine came out, MIT expected to get one. In the early sixties, the deal was that MIT got one 8-hour shift, all the other New England colleges and universities got a shift, and the third shift was available to IBM for its own use. One use IBM made of its share was yacht handicapping: the President of IBM raced big yachts on Long Island Sound, and these boats were assigned handicap points by a complicated formula. There was a special job deck kept at the MIT Computation Center, and if a request came in to run it, operators were to stop whatever was running on the machine and do the yacht handicapping job immediately.”

  • Using Ring 5, Randy Saunders.

    "All Multics User functions work in Ring 5." I have that EMail (from Dave Bergum) framed on my wall to this date. … All the documentation clearly states that system software has ring brackets of [1,5,5] so that it runs equally in both rings 4 and 5. However, the PL/I compiler creates segments with ring brackets of [4,4,4] by default. … I found each and every place CNO had fixed a program without resetting the ring brackets correctly. It started out 5 a day, and in 3 months it was down to one a week.”

• Bell Systems Technical Journal 57(6) Part 2: Unix Time-sharing System (July–August 1978)

  This volume contains some of the first broadly-accessible descriptions of Unix. Individual articles are available on archive.org. As of late January 2021, you can buy a physical copy on Amazon for $2,996. Interesting articles include Thompson on Unix implementation, Ritchie’s retrospective, and several articles on actual applications, especially document preparation.