There Really Was a Bug in the Computer

9 September 1947, Harvard University in the United States.

A group of engineers were debugging the Harvard Mark II. It looked nothing like the computers we know today. There was no screen, no mouse, and its interior was packed with relays. While it ran, it produced a constant series of mechanical clicks.

That day, the machine developed a problem.

The engineers began investigating. There was no such thing as one-click diagnostics, let alone a search engine they could ask. They could only trace the circuits and relays, one component at a time.

Eventually, they found the cause inside one of the relays.

It was a moth.

It had become lodged between the relay contacts, interfering with the machine’s operation.

The engineers carefully removed the moth. Instead of throwing it away, they taped it into that day’s operational log and wrote a note beside it, to the effect that this was the first time an actual “bug” had been found.

Grace Hopper, who was working with the Mark II team at the time, often told the story in later years. The unfortunate moth entered the history of computing along with her. The logbook and the moth are still held by the Smithsonian’s National Museum of American History in the United States.

Today, when programmers say, “There’s a bug here,” they usually mean that something is wrong with the program.

But on one day in 1947, the bug inside the computer really was an insect.

It may well have been the most literal malfunction in the history of computing.