Z3: the First Functional Programm-Controlled Automatic Calculating Machine

Zuse’s conditional combinatory logic and abstract switching techniques enabled him to make a direct reconstruction of the Z1 as a relay calculator. In this, he took the advice of his friend Schreyer. Starting in 1938, Zuse built an arithmetic unit, later called the Z2, using relays. This experimental device provided him with valuable experience.
In mid 1940, Zuse begann building the Z3. It was operational in May 1941. The arithmetic unit was electromechanical, constructed of 600 relays: the store used 1400 relays.
The Z3 cost about 25,000 reichsmark. It was damaged in an air raid in 1943, and destroyed in 1944. The 1941 Z3 was the first fully functional, freely programmable binary automatic computer. The programm sequence consisted of just one loop.