The Z1, Z2, Z3, and Z4: His computers should be free programmable, it means that they should read arbitrary instructions from a punch tape, they should work in the binary digit system because Zuse wanted to contruct his computer with binary switching elements.
His first machine, which worked on these principles, was construction from 1936-1938 (Z1). The Z1 was a machine with a 64 cell (word) memory a 32 bits and the components as discussed above. The Z1 consisted completely of metal sheets. The clock frequency was around one Hertz. The Z1 is the first programable machine of the world.
Unsatisfied with the reliability of the binary switching metal sheets he constructed the Z2. The Z2 used the mechanical memory of the Z1, but for the arithmetic and control unit he used relays (800 relays) from the phone companies.
It is undisputed today, that the Z3 was the first free programmable, based on a binary floating system, working computer of the world.
The goal of the Z4 - developed between 1942 and 1945 - was a prototype of a series. The Worldwar 2 detroyed Konrad Zuse's hope, that his mchines should support the work of engineers.