MIT Differential Analyzer

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The Differential Analyzer was MIT's first computer, built by Vannevar Bush and his students in the early 1930s. Jane Pickering of the MIT Museum and I are working on a project to build a working replica of the device for historical and educational purposes. It was an analog computer, primarily used for evaluating and solving differential equations by mechanical integration. In my book on control systems, there is a chapter on the Differential Analyzer; many who worked on the machine (e.g. Harold Hazen, Gordon Brown, Claude Shannon) later made contributions to feedback control, information theory, and computing. (Photos courtesy MIT Museum)

Overall view of the Differential Analyzer. The integrator units (six of them) are inside the wood and glass boxes at left, the bus rods which carry numerical information are in the center, and the input and output tables are at right. In the foreground is a numerical tabulator which converted shaft positions to printed numerical output. Samuel Caldwell is standing at left.

Operator's console of the Differential Analyzer, a literally "graphical" user interface. The operator (at left, Samuel Caldwell) manipulates a pointer by hand to follow the curves on the paper, which are then integrated or otherwise processed by the machine, which drives a plotter to make another graph as output.. Vannevar Bush is looking on.

Close-up of wheel and disk integrators on the machine. The motor-like devices on the left are "Nieman Torque Amplifiers," capstan-driven devices which act as mechanical amplifiers to keep the remaining calculations from loading the integrators (and hence losing accuracy).

Close up of bus rods which carry variables between different calculating units. Variables are encoded as shaft positions (in rotation). The machine is programmed by rearranging these rods and gears, requiring a new assembly for each set of calculations. The rods also add and multiply, using gearing between them. Note the Nieman torque amplifiers at left.