Differential analyzer
More info
- Creator
- Vannevar Bush, MIT
- Released
- 1931
- Type
- Mechanical analog computer
A room-sized assembly of shafts and gears that solved differential equations by physically performing them — computing in rotation rather than in digits.
Vannevar Bush built the first at MIT in 1931. Its heart is the wheel-and-disc integrator, a mechanism borrowed from nineteenth-century tide-predicting machines: a small wheel rides against a spinning disc, and its distance from the centre sets the ratio. Drive that distance from one quantity and the mechanism integrates it, continuously, without ever representing a number. Six integrators coupled by shafts handled equations that otherwise took weeks by hand.
Programming meant taking the machine apart. Reconfiguring it for a new problem took a couple of days of physically connecting shafts in the order the equation demanded. Accuracy was capped at a few significant figures by backlash and slip, which is the founding problem of analog computing: the error is indistinguishable from the signal.
The Army's Ballistic Research Laboratory at Aberdeen acquired its own copy to compute firing tables — the exact workload that would justify building ENIAC a few years later. Claude Shannon was the graduate student who reconfigured the MIT machine, and the wiring of its control circuits gave him the subject of his master's thesis on Boolean algebra in relay networks. Douglas Hartree in Manchester built a working analyzer out of Meccano in 1934 for about twenty pounds.