Computer pioneer Grace Hopper often recounted the story of her team finding the first physical computer bug:

While she was working on a Mark II Computer at Harvard University in 1947, her associates discovered a moth that was stuck in a relay; the moth impeded the operation of the relay. While neither Hopper nor her crew mentioned the phrase "debugging" in their logs, the case was held as an instance of literal "debugging." For many years, the term bug had been in use in engineering. The remains of the moth can be found in the group's log book at the Smithsonian Institution's National Museum of American History in Washington, D.C.

The photo below of the log book states "Relay #70 Panel F". What precise function did this relay perform?

first computer bug

  • 4
    This question might be "Are there schematics for the Mark II?"
    – RETRAC
    Oct 30 '20 at 1:09
  • 5
    @RETRAC: There are, in the Grace Murray Hopper Collection of the Smithsonian. Here are links to the Mark II panel diagram and a badly-organized PDF of random pages from the Mark II User's Manual, with schematics of various parts. However, I haven't yet found the relay in question.
    – DrSheldon
    Oct 30 '20 at 1:23
  • 17
    "What precise function did this relay perform?" - in this instance it caught a moth. Do you mean what function was the relay supposed to perform? Oct 30 '20 at 4:34
  • 5
    @BruceAbbott wouldn't that make it a feature and not a bug?
    – HorusKol
    Oct 31 '20 at 5:26
  • 4
    I am not sure it is entirely meaningful to ask. A relay is a mechanical switch; it is either open or closed, that's it. So it can store 1 bit. The Harvard Mark II was not a stored-program computer; it read instructions from a paper tape and did the calculations. It was a bit more like an automated calculator. So what did that one bit in its memory do? It stored one bit of a number, either one to be operated on or the output of an arithmetic operation. That's probably about as much as can be said. Jan 17 at 18:49

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