Harvard Mark II

The Harvard Mark II, also called the Aiken Relay Calculator, was an electromechanical computer built under the direction of Howard Aiken at Harvard University and completed in 1947. The Navy financed it, and after it was debugged in September 1947 it was delivered to the Naval Proving Ground at Dahlgren, Virginia, where it was used for ballistic calculations. It followed Aiken's Mark I but replaced that machine's electromechanical counters with high-speed electromagnetic relays, which made addition about 2.6 times faster and multiplication about 8 times faster. It weighed roughly 25 short tons and had built-in hardware for functions such as reciprocal, square root, logarithm and exponential. Like the Mark I it was not a stored-program machine and read its instructions one at a time from tape. It is also remembered for the log book entry of September 9, 1947, in which a moth found in the machine was taped in as the first actual case of a bug being found.