History of Computers: The Z3 (Completed on December 5, 1941) was controlled by punched tape, using discarded movie film, while the input and output were via the same four-decimal-place keyboard and lamp display. The entire machine was based on relay technology, about 2,600 of them being required, 1,400 for the memory, 600 for the arithmetic unit, and the rest as part of the control circuits. They were mounted in three racks, two for the memory and one for the arithmetic and control units, each about 6 feet high by 3 feet wide.

The 64-word memory was floating-point binary in organization but this time the word length was increased to 22 bits: 14 for the mantissa, 7 for the exponent, and one for the sign.

The speed of the Z3 was comparable to that of the Harvard Mark I. The Z3 could perform three or four additions per second and multiply two numbers together in 4 to 5 seconds. The Z3's floating point representation of numbers made it more flexible then the Mark I. Started in 1939, the Z3 was operational by December 5, 1941. The total cost of materials was 25,00 RM (about $6,500 at the time). It was never used for any large problems because its limited memory would not enable it to hold enough information to be clearly superior to the manual methods for solving a system of linear equations. It remained in Zuse's house until it was destroyed in an air raid in 1944. The Z3 was the first machine in the world that could be said to be a fully working computer with automatic control of its operations.