In 1934, driven by his dislike of the time-consuming calculations he had to perform as a civil engineer, Konrad Zuse began to formulate his first ideas on computing. His feeling was that such stupid calculations should be performed by machines and not by human beings. The first question he posed in 1934 was:
What mathematical problems should a computing machine solve?
His answer was the following definition of computing (1936):
To build new specifications from given specifications by a prescription.
In the year 1943 he extended the definition to:
Computing is the deviation of result specifications to any specifications by a prescription.
From these definitions, Konrad Zuse defined the logical architecture of his Z1, Z2, Z3, and Z4 computers From the beginning it was clear for him that his computers should be freely programmable, which means that they should be able to read an arbitrary meaningful sequence of instructions from a punch tape. It was also clear to him that the machines should work in the binary number system, because he wanted to construct his computers using binary switching elements. Not only should the numbers be represented in a binary form, but the whole logic of the machine should work using a binary switching mechanism (0-1-principle).
He planned a high performance binary floating point unit in the semi-logarithmic representation, which would allow him to calculate very small and very big numbers with sufficient precision.
He implemented a high performance adder with a one-step carry-ahead and precise arithmetic exceptions handling.
He developed a memory in which each cell could be addressed by the punch tape and could store arbitrary data.
Finally, he constructed a control unit that controlled the whole machine, and implemented input and output devices from the binary to the decimal number system and vice versa. In Part 3 we'll start to take a closer look at these machines.
Fig.6. Konrad Zuse working
on a Z4 Computer (1942).