Harvard Mark II

It was completed and debugged in 1947, and delivered to the US Navy Proving Ground at Dahlgren, Virginia in March 1948,[5] becoming fully operational by the end of that year.

Additionally, the Mark II was actually composed of two sub-computers that could either work in tandem or operate on separate functions, to cross-check results and debug malfunctions.

The Mark II had a peculiar programming method that was devised to ensure that the contents of a register were available when needed.

[9] The Mark II is also known for being the computer with the first recorded instance of an actual bug (a moth) disrupting its operation.

The insect was extracted from the machine's electronics and taped to the log book, with the note "first actual case of [a] bug being found", on September 9, 1947.