Multiprogramming and Time Sharing

This lesson briefly discusses the history of multiprogramming and time sharing and the approaches taken to implement time sharing.

History of multiprogramming and time sharing

After a time, because machines were expensive, people began to share machines more effectively. Thus the era of multiprogramming was born"Programming Semantics for Multiprogrammed Computations" by Jack B. Dennis, Earl C. Van Horn. Communications of the ACM, Volume 9, Number 3, March 1966. An early paper (but not the first) on multiprogramming., in which multiple processes were ready to run at a given time, and the OS would switch between them, for example when one decided to perform an I/O. Doing so increased the effective utilization of the CPU. Such increases in efficiency were particularly important in those days where each machine cost hundreds of thousands or even millions of dollars (and you thought your Mac was expensive!). Soon enough, however, people began demanding more of machines, and the era of time sharing was born1. [S59]“Time Sharing in Large Fast Computers” by C. Strachey. Proceedings of the International Conference on Information Processing, UNESCO, June 1959. One of the earliest references on time-sharing. 2.[L60] “Man-Computer Symbiosis” by J. C. R. Licklider. IRE Transactions on Human Factors in Electronics, HFE-1:1, March 1960. A funky paper about how computers and people are going to enter into a symbiotic age; clearly well ahead of its time but a fascinating read nonetheless. 3.[M62] “Time-Sharing Computer Systems” by J. McCarthy. Management and the Computer of the Future, MIT Press, Cambridge, MA, 1962. Probably McCarthy’s earliest recorded paper on time sharing. In another paper [M83], he claims to have been thinking of the idea since 1957. McCarthy left the systems area and went on to become a giant in Artificial Intelligence at Stanford, including the creation of the LISP programming language. See McCarthy’s home page for more info: 4. [M83] “Reminiscences on the History of Time Sharing” by John McCarthy. 1983. Available: terrific historical note on where the idea of time-sharing might have come fzshortm, including some doubts towards those who cite Strachey’s work [S59] as the by pioneering work in this area.. Specifically, many realized the limitations of batch computing, particularly on programmers themselves“Introduction and Overview of the Multics System” by F. J. Corbato, V. A. Vyssotsky. Fall Joint Computer Conference, 1965. A great early Multics paper. Here is the great quote about time sharing: “The impetus for time-sharing first arose from professional programmers because of their constant frustration in debugging programs at batch processing installations. Thus, the original goal was to time-share computers to allow simultaneous access by several persons while giving to each of them the illusion of having the whole machine at his disposal.”, who were tired of long (and hence ineffective) program-debug cycles. The notion of interactivity became important, as many users might be concurrently using a machine, each waiting for (or hoping for) a timely response from their currently-executing tasks.

Implementing time sharing

One way to implement time sharing would be to run one process for a short while, giving it full access to all memory (see figure below), then stop it, save all of its state to some kind of disk (including all of physical memory), load some other process’s state, run it for a while, and thus implement some kind of crude sharing of the machine“A Time-Sharing Debugging System for a Small Computer” by J. McCarthy, S. Boilen, E. Fredkin, J. C. R. Licklider. AFIPS ’63 (Spring), New York, NY, May 1963. A great early example of a system that swapped program memory to the “drum” when the program wasn’t running, and then back into “core” memory when it was about to be run..

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