“This type of design is called restoring logic, and the example in hydraulic technology is particularly interesting, because it corresponds almost exactly to the logic used in modern electronic computers. The water pressure in the pipes is analogous to the voltage on the wires, and the hydraulic valve is analogous to the metal-oxide transistor. The control, input, and output connections on the valve correspond closely to the three connections (called gate, source, and drain) on a transistor.”