Analog computer

An analog computer represents quantities with continuously varying physical values and computes by physically modeling relationships among those quantities.

Operational amplifier: An electronic amplifier whose feedback circuits can produce precise mathematical operations on voltages. Its circuits let electronic analog computers add, integrate, and scale voltage signals.
Differential equation: An equation relating an unknown function to one or more of its derivatives. Analog computers can solve these equations by constructing circuits that mirror their terms.
Antikythera mechanism: An ancient Greek geared device that modeled astronomical cycles and predicted celestial events. Its geared model of recurring motions is an early example of mechanical analog computation.
Digital computer: A computer that represents information with discrete symbols, usually binary digits, and processes them through logical operations. Digital computers encode quantities discretely rather than as continuously varying physical values.
Simulation: The imitation of a system's behavior over time using a model. Analog computing made simulation a direct physical process rather than a sequence of symbolic calculations.
Integrator: A circuit or device whose output accumulates its input over time. Integration lets an analog computer represent changing quantities and solve differential equations.
Flight simulator: A system that reproduces aircraft behavior and operating conditions for training or testing. Analog computers modeled aircraft dynamics before digital simulation became practical.
James Thomson: A Scottish engineer who developed a mechanical integrator for calculating the area under a curve. His integrator supplied a key operation for later differential analyzers.
Hybrid computer: A computer combining analog components for continuous signals with digital components for discrete processing. Hybrid systems combine analog simulation with digital control, storage, or calculation.
Control theory: The study of how to regulate dynamic systems using feedback and control inputs. Analog circuits both implemented control laws and helped engineers study feedback behavior.

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