Stibitz demonstrates remote computing, September 11, 1940

-September 11, 2017

George Stibitz of Bell Telephone Laboratories used his Complex Number Calculator (CNC) to demonstrate remote computing for the first time on September 11, 1940* when a series of math problems were transmitted over a phone line to the computer, which promptly returned the answers via teletype.

Stibitz was a member of a group of mathematicians who designed relay switching equipment when he observed the similarity between the circuit paths through relays and the binary notation for numbers.

Stibitz binary adder
A replica of Stibitz's binary adder, which he built in his kitchen. Source: Reference 1
In 1937, he took a few telephone relays home and fastened two of the relays to a board, cut strips from a tobacco can and nailed them to the board for input. He used a dry cell and a few flashlight bulbs for output, and wired a binary adder (see photo of a replica of his homemade adder).

He recalled: "I wired the relays to give the binary digits of the sum of two one-digit binary numbers, which were entered into the arithmetic unit by pressing switches made of the metal strips. The two-flashlight-bulb output lighted up to indicate a binary 1 and remained dark for binary 0."

After the "kitchen adder," Stibitz designed more sophisticated circuits that could subtract, multiply, and divide. Bell Labs then asked him to work on a relay calculator for complex arithmetic that could be used by a group that designed noise filters and amplifying circuits for long distance telephone lines, who needed to solve innumerable algebraic equations with complex numbers. Until then, the company employed a small team of women computers with ordinary desk calculators.

CNC Model IStibitz designed the Model I CNC (photo) with switching engineer Samuel B Williams, and it was constructed in 1939 at a cost of about $20,000.

It was not programmable, as a combination of relay circuits permanently controlled its sequence of operations. The machine used a decimal system with the decimal point fixed at the beginning of each number. It had a panel containing about 450 relays to perform computations, and a teletype with a special keyboard to enter mathematical problems and record the answers

Stibitz was among a handful of engineers across the globe designing machines that involved using relays to implement binary logic at the time.

The demonstration occurred at a meeting of the American Mathematical Society at Dartmouth College in Hanover, NH, just a few hundred miles north of the Bell Labs building in New York, where the CNC sat. Since the teletype was connected by cable, the Model I could be used from any point in the phone system.

The computer connected by telephone lines (28-wire teletype cable) to a teletype unit installed at the college. Attendees of the meeting suggested equations that an attendant entered into the teletype unit to be transmitted and calculated remotely. Correct answers were returned approximately a minute later to what was described as an astounded audience.

Although history records the demonstration as a success, remote access of this type was not repeated for another 10 years. Notably, US involvement in World War II began in December 1941 and much of the resources that would have been devoted to making advances in this area were moved to military and defense projects.

*The majority of records of this event indicate a date of September 11, 1940, however, some records, including a plaque at Dartmouth College, indicate a date of September 9, 1940.

  1. Stibitz calculators at Bell Labs,

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For more moments in tech history, see this blog. EDN strives to be historically accurate with these postings. Should you see an error, please notify us.

Editor's note: This article was originally posted on September 11, 2012 and edited on September 11, 2017.

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