ENIAC
The ENIAC was first designed to print firing tables for U.S. Army artillery, but the war ended before the machine was completed. Instead, its first real job (not test) was to calculate how neutrons would go through various materials. This was needed in making a hydrogen bomb. ENIAC took 70 hours to work out pi to 2000 decimal places. A modern PC with a CPU of the size of 2x2 cm is much faster than ENIAC, which used up a whole room of space. For an example, a modern PC can work out a million (1,000,000) decimal places of pi in about ten seconds.