Konrad Zuse's Legacy: The Architecture of the Z1 and Z3

This paper provides a detailed description of the architecture of the Z1 and Z3 computing machines that Konrad Zuse designed in Berlin between 1936 and 1941. The necessary basic information was obtained from a careful evaluation of the patent application Zuse filed in 1941. Additional insight was gained from a software simulation of the machine’s logic. The Z1 was built using purely mechanical components; the Z3 used electromechanical relays. However, both machines shared a common logical structure, and their programming model was the same. I argue that both the Z1 and the Z3 possessed features akin to those of modern computers: The memory and processor were separate units, and the processor could handle floating-point numbers and compute the four basic arithmetical operations as well as the square root of a number. The program was stored on punched tape and was read sequentially. In the last section of this paper, I put the architecture of the Z1 and Z3 into historical perspective by offering a comparison with computing machines built in other countries.