Overview

The term computer today implies a stored-program electronic digital computer, but it has not always had that meaning. Fifty years ago, before the introduction of the modern solid-state computer, the word could mean any of many different kinds of electromechanical and electronic analog machines capable of computation. Application-specific analog computers, built from gears, levers, clutches, and motors, played an important role in World War II for setting fuses and gun elevations for artillery while accounting for such factors as range, elevation angle, propellant, wind, weather, and even the spin of the earth. Data was entered in these computers with knobs and hand cranks, and the useful output data appeared on dials or it controlled mechanical movements. It is significant that the first use of the large digital computers built by the U.S. government during the war was the preparation of tables for calculating artillery trajectories.

As the first vacuum-tube digital computers were being developed, engineers and scientists were using analog computers, consisting largely of operational amplifiers and precision potentiometers, to solve mathematical problems and perform simulations. Data was entered by setting banks of potentiometers, and the output could be in the form of meter readings, oscilloscope waveforms, or graphs on x-y plotters. The early analog computers had vacuum-tube circuitry, but these were later transistorized. Analog computers played a significant role in the design and testing of NASA equipment and the simulation of space vehicle behavior in the early days of the space program. They were also widely...