What Happened on May 12th
Konrad Zuse completes his Z3 computer, the first program-controlled electromechanical digital computer. It followed in the footsteps of the Z1 - the world’s first binary digital computer - which Zuse had developed in 1938. Much of Zuse’s work was destroyed in World War II, although the Z4, the most sophisticated of his creations, survives.
The first appropriation was made to the construction of the Harvard Mark I, eventually completed in 1944. The Mark I was the first successful fully automatic machine and computed three additions or subtractions a second; its memory stored 72 numbers of 23 digits (plus sign).