# Princeton (Cambridge Computing)

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When Alan Turing is nearing completion of his Ph.D. dissertation in 1938 he is offered a job by John von Neumann. If Turing returns to England, he can continue on his research fellowship at Cambridge. While trying to decide if he should accept von Neumann's offer, Turing's research advisor (Alonzo Church) shows Turing a copy of Claude E. Shannon's journal article describing the key results from his Masters degree thesis. By this time, Turing has begun working in Princeton's physics department workshop on key electronic components for a prototype computer circuit. Shannon's work on how to do Boolean algebra using electronic circuits is clearly an example of how to put into hardware the logical subsystems of a Universal Turing Machine.

Turing arranges for Shannon to visit Princeton and give a lecture on his thesis work. Turing shows Shannon the partially completed electronic computer components that he has been building and explains the concept of a Universal Turing Machine. Shannon decides to do his Ph.D. research in Princeton working with Turing. Shannon first completes the digital calculating circuit that Turing has already started to construct then builds the special purpose computer to calculate the Riemann zeta-function, a calculating device that Turing has long dreamed of constructing. In order to continue working with Shannon on this computer, Turing takes the job offer from von Neumann, delaying his return to England until after England enters the war.

The ability of Shannon and Turing to quickly produce a functioning electronic computer depended on support from Shannon's masters thesis adviser Vannevar Bush and Turing's new boss, von Neumann. It was only after the defeat of Nazi Germany when Turing learned the fact that Shannon already had a U.S. government security clearance as Bush's student. While at Princeton, the electronic components Shannon explained as coming from "the electronic shop at M.I.T." were actually from U.S. corporations working under government contract on military electronics research. For most of the electronic components used by Shannon and Turing, a request from Shannon to the office of either Bush or von Neumann would result in delivery of the items within a week, often by military currier. The physical nature of the silicon carbide circuit components was a military top secret. It should be noted that Turing was able to recognize the silicon carbide components because of his familiarity with European crystal radio technology. John von Neumann arranged that the physics department workshop was also quickly provided with six new research assistants who worked under Shannon assembling and testing the analog circuits of Turing's zeta function machine.

Continue to a peak at the key circuit of the Shannon-Turing zeta function computer.