A Symbolic Analysis of Relay and Switching Circuits

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"A Symbolic Analysis of Relay and Switching Circuits" is the title of a master's thesis written by computer science pioneer Claude E. Shannon while attending the Massachusetts Institute of Technology (MIT) in 1937. In his thesis, Shannon, a dual degree graduate of the University of Michigan, proved that Boolean algebra[1] could be used to simplify the arrangement of the relays that were the building blocks of the electromechanical automatic telephone exchanges of the day. Shannon went on to prove that it should also be possible to use arrangements of relays to solve Boolean algebra problems.

The utilization of the binary properties of electrical switches to perform logic functions is the basic concept that underlies all electronic digital computer designs. Shannon's thesis became the foundation of practical digital circuit design when it became widely known among the electrical engineering community during and after World War II. At the time, the methods employed to design logic circuits (for example, contemporary Konrad Zuse's Z1) were ad hoc in nature and lacked the theoretical discipline that Shannon's paper supplied to later projects.

Psychologist Howard Gardner described Shannon's thesis as "possibly the most important, and also the most famous, master's thesis of the century".[2] A version of the paper was published in the 1938 issue of the Transactions of the American Institute of Electrical Engineers,[3] and in 1940, it earned Shannon the Alfred Noble American Institute of American Engineers Award.


  1. ^ Caldwell, Samuel H. (1965) [1958]. Switching Circuits and Logical Design, Sixth Printing. New York: John Wiley & Sons. p. 34. ISBN 978-0471129691. [Shannon] constructed a calculus based on a set of postulates which described basic switching ideas; e.g., an open circuit in series with an open circuit is an open circuit. Then he showed that his calculus was equivalent to certain elementary parts of the calculus of propositions, which in turn was derived from the algebra of logic developed by George Boole.
  2. ^ Gardner, Howard (1987). The Mind's New Science: A History of the Cognitive Revolution. Basic Books. p. 144. ISBN 0-465-04635-5.
  3. ^ Shannon, C. E. (1938). "A Symbolic Analysis of Relay and Switching Circuits" (PDF). Trans. AIEE. 57 (12): 713–723. doi:10.1109/T-AIEE.1938.5057767. hdl:1721.1/11173. S2CID 51638483.

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