Every developer who has ever muttered "there is a bug in this" is repeating a word with a surprisingly literal origin. On September 9, 1947, the operators of the Harvard Mark II, an early electromechanical computer, traced a malfunction to its source and found something they did not expect: a moth wedged inside Relay #70. They removed the insect, taped it into the operations logbook, and wrote a now-famous line beside it: "First actual case of bug being found." That page, moth and all, survives today in the collection of the Smithsonian's National Museum of American History.
It is one of the best-loved stories in computing, and like most good stories it is a little more complicated than the popular version. Worth getting right, because the discipline it gave us is the same one behind every connected device we build.
What actually happened in 1947
The Mark II was a room-sized machine built from relays, switches, and thousands of moving parts. When a moth flew into one of those relays, it physically interfered with the contacts and caused a fault. The technicians who found it had a sense of humor: calling it the "first actual case of bug being found" was a joke precisely because engineers had already been using "bug" for years to describe mysterious faults in machinery. Thomas Edison used the term in his notebooks back in the 1870s.
