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Eckert and Mauchly: Electronic Numerical Integrator And Computer (ENIAC), 1949

Control Issues

The biggest challenge facing Mauchly and Eckert was devising a means to control the circuits responsible for counting the electronic pulses. The basic science of getting circuits to count had already been developed, but Eckert and Mauchly had to ensure that the right pulses got to the right circuits, and that the circuits counted in the right order at the right time.

The ENIAC team began working on the accumulators of the machine first. An accumulator is a kind of register that receives a number and produces and stores the results of arithmetic operations of the given number with other numbers. The accumulators in ENIAC were designed not only to store numbers, but were also able to add and subtract them and transmit them to other units of the machine. By connecting the wires carrying data from one accumulator to the wires controlling operations in another, the ENIAC could control those operations based on the content of its data. These types of operations are known, even today, as "data-sensitive operations," and the ENIAC was probably the first electronic machine to be able to perform such operations.

Since the accumulators could store a number with as many as ten digits, Eckert and Mauchly split each digit of a given number into its own circuit, rather than building the accumulator to count electronic pulses to reach a number. This meant that the number 444, for example, did not require 444 pulses in order to be represented electronically within ENIAC. Rather, it required 4 pulses in the hundreds circuit, 4 in the tens circuit, and 4 in the ones circuit—a total of 12 pulses instead of 444. This design greatly increased the speed of the machine. Though its structure was large and included many components, the simplicity and practicality of ENIAC's design was what enabled the master programmer to exert the control necessary for the success of the computer.

The men and women on the ENIAC design and programming teams worked tirelessly to make the machine a success. From left to right, pictured here are: Homer Spence; J. Presper Eckert, chief engineer; Dr. John W. Mauchly, consulting engineer; Elizabeth Jennings; Capt. Herman H. Goldstine, liaison officer; Ruth Lichterman.