Monday, June 21, 2004

Dan Bricklin: Multics reunion and honoring Prof. Corbato

Dan Bricklin: Multics reunion and honoring Prof. Corbato: "Yesterday I attended the Multics Reunion at MIT. It consisted of a symposium during the day and a dinner in the evening honoring the head of the project, Prof. Fernando J. Corbato (known to all as Corby). Multics was a major OS project started in 1965, which influenced many operating systems since, most notably Unix. I worked on it from January 1970 until September 1973. It is where I met Bob Frankston.
Why was Multics so secure? Several reasons, including: Buffer overflows are the single most common source of security vulnerabilities today, but Multics didn't have them. Why: The system was written in PL/I, not C, which handles oversize strings well. The hardware was used (unlike today's x86's) to keep execute bits off on data and to make address overflows fault or wrap back into data and not code or other data. Stacks grew in a positive direction, not negative like today, making it hard to overwrite subroutine return information (the common exploit today). Also, security was a primary goal of Multics, built in from the first -- it was not an option."

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