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Eccles & Jordan Invent the Flip-Flop Circuit, the Basis for Electronic Memory

Flip-flop schematics from the Eccles and Jordan patent filed 1918,

Flip-flop schematics from the Eccles and Jordan patent filed 1918, one drawn as a cascade of amplifiers with a positive feedback path, and the other as a symmetric cross-coupled pair

On June 21, 1918 British physicists and professors of engineering at London's City and Guilds Technical College William Henry Eccles and Frank Wilfred Jordan filed a patent for "Improvements in Ionic Relays." The patent specification 148,582 was published in 1920. It was initially called the Eccles–Jordan trigger circuit and consisted of two active elements (vacuum tubes).  

Early flip-flops were known variously as trigger circuits or multivibrators. Prior to the invention of electronic computing Eccles and Jordan viewed their invention as a "method of relaying or magnifying in electrical ciruits for use in telegraphy and telephony." However, a flip-flop circuit has two stable states and, as Claude Shannon pointed out in his Mathematical Theory of Communication (1948), a flip-flop can be used to store one bit of information. Flip-flop circuits operate using Boolean algebra (AND, OR, NOT). Thus, with the invention of electronic computing using vacuum tubes as switches, flip-flops became the basic storage element in sequential logic used in digital circuitry, and the basis for electronic memory. The design was probably first applied to computing in the 1943 British Colossus codebreaking computer (1943).

In September 1919 Eccles and Jordan described the flip-flop in a brief one-page paper, "A trigger relay utilizing three-electrode thermionic vacuum tubes," The Electrician, vol. 83, (September 19, 1919) p. 298. However, the patent, filed the previous year, and consisting of 5 pages, remains the first description of this invention.

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