IBM Relay Calculator

IBM Relay Calculator

In December 1944, IBM delivered to the U.S. Army Ballistic Research Laboratory's Aberdeen Proving Ground two "Aberdeen Relay Calculators" that were more than 30 times faster than an IBM 601 electromechanical multiplier. Developed in less than two years by an engineering team under Clair D. Lake,, the Relay Calculator served as the fastest digital calculator in the United States during the last months of World War II. It was used for determining the trajectories of artillery shells.

IBM Relay Calculator
The Relay Calculator had a capacity of six digits in the multiplier and six digits in the multiplicand in multiplication. It ran at 100 card cycles per minute on single multiplication or cross-adding operations; combinations of two or three multiplications and cross-adding were performed on a two-cycle basis at 50 cards a minute. The machine was basically a reproducer to which had been added a full set of brushes one card cycle in advance of the punch station and modified so that the read unit was independent of the punch unit. The standard 45-column checking unit was used and all standard reproducer functions were available. Calculating was performed by a separate relay unit connected to the reproducer by four detachable plug-in type connector cables.

The machine contained 161 counter positions arranged into 20 counter groups designated as multiplier counter, multiplicand counter and counters 1-18. Two separate buses were provided for connecting the various counter groups so that amounts could be transferred from one group to another. The use of two busses allowed two sets of values to be transferred by the different sets of counters simultaneously.


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