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This month in tech history: September - First computer "bug" found (literally)

9 September 1947 – Moth vs. Harvard Mark II

Ever wondered why the term ‘bug’ is so popular in the computing world?

In 1947, Grace Murray Hopper was working on the Harvard University Mark II Aiken Relay Calculator.

Hopper, or “Amazing Grace” as she was known, was one of the first computer geeks, and created the first compiler for a computer programming language as well as working on the development of COBOL. The Cray XE6 “Hopper” supercomputer at NERSC was named for her, and she also coined the phrase “It’s easier to ask forgiveness than it is to get permission”.

On the 9th of September, the Mark II began experiencing problems. An investigation discovered a moth trapped between the points of Relay #70, in Panel F.

In those early days of computing, computers would fill a room and the warmth created by the internal components attracted moths, flies etc., which would then short circuits and cause the computer to crash.

The Mark II operators removed the moth and included it in their log. The corresponding entry reads: “First actual case of bug being found.”


Word went out that they had “debugged” the machine and the term increased in popularity. Hopper didn’t actually find the insect herself, as she readily acknowledged, but she liked to recount the story so much that it is often attributed to her.

The term ‘bug’, while often attributed to Hopper, in fact originates not with computer pioneers, but with much earlier engineers. The first example cited in the Oxford English Dictionary is from the Pall Mall Gazette of 11 March 1889:

Mr. Edison, I was informed, had been up the two previous nights discovering 'a bug' in his phonograph - an expression for solving a difficulty, and implying that some imaginary insect has secreted itself inside and is causing all the trouble.

The original log book, complete with the late moth, is part of the collection of the Smithsonian National Museum of American History, though sadly, it is not currently on display.

So, next time your computer or smartphone crashes and you suspect a bug, think about the poor nameless moth whose discovery made the term popular.


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Kate Hoy

Kate Hoy is Editor of IDG Connect

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