Harvard Mark I

What Does Harvard Mark I Mean?

The Harvard Mark I was an electromechanical computer developed by Howard Aiken at Harvard University and built by IBM in 1944. The computer was 55 feet long, eight feet high and weighed five tons. It provided vital calculations for the U.S. Navy during World War II (WWII) and was the first of a series of computers designed by Aiken. At the time, it was touted as the world’s first programmable computer, although it was actually preceded by the 1941 release of the German Konrad Zuse’s Z3 model.


The Harvard Mark I was also known as the IBM Automatic Sequence Controlled Calculator (ASCC).

Techopedia Explains Harvard Mark I

The Harvard Mark I could perform four arithmetic operations and had built-in programs for processing logarithms and trigonometric functions. The Mark I received instructions on paper tape and loaded data output on punch cards.

In the 1940s, mathematician and U.S. Navy Rear Admiral Grace Hopper joined the Harvard team and was charged with keeping the Mark I running. It is believed that Hopper gave rise to the term "debug" when she fixed a malfunctioning Mark II by removing a moth trapped in the machine’s electromechanical innards.

The Mark I remained in use at Harvard until 1959, at which time its technology was already far surpassed by fully electronic computers.

The Mark I was followed by the Mark II, Mark III and Mark IV.


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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.