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

Slogging Through Analog Calculations

The Differential Analyzer was "analog" rather than "digital." This means that it got to the correct answer by moving a distance specified by the numbers plugged into a given differential equation. The machine received these numbers through its input tables, into which operators fed numbers and functions. Different units performed different mathematical operations (addition, multiplication, subtraction and division), and different units could be connected in a certain sequence by long shafts. The way in which the connections were made determined how the machine would solve the problem. The machine was less accurate than a "digital," or electronic, machine would have been because the solutions it provided were estimates. In addition, as time wore down its many gears and pulleys, the machine grew inaccurate.

Despite its shortcomings, the Differential Analyzer was the most sophisticated calculating device of its time. Furthermore, it helped establish the notion that using electricity to make calculations would provide the fastest and most accurate results possible. The first company to use electricity as a source of speed and accuracy had its roots in the work of Alexander Graham Bell: in the mid-1930s, Bell Telephone Laboratories succeeded in turning the numbers dialed into telephones and the sound transmitted over telephone wires into electrical signals.

Letter from John C. Sims, Jr. to Dr. Frazer, Accompanied an original enclosure of a brief paper covering the history of electronic computer development. References original enclosure of a book loaned to Dr. Frazer. (684k). 5/21/1948. Page 2 of 2, (719k)

Letter from Lt. Col. P. N. Gillon to Mr. John Frazer, Responds to request for opinion and comments about the ENIAC. (940k). 5/24/1948. Page 2 of 2, (677k)