Logic gates and Boolean algebra

In 1854 George Boole published An Investigation of the Laws of Thought, an algebra in which variables take only two values and the operations follow rules much like arithmetic. For more than eighty years it was a topic for logicians.

In 1937 Claude Shannon, a master's student at MIT, noticed that the relay switching circuits in telephone exchanges obeyed exactly the same rules: switches in series behave like AND, in parallel like OR. His thesis, published in 1938, turned circuit design into algebra. Every processor is built on that observation.