On Konrad Zuse’s Developments

Konrad Zuse, a German engineer, did pioneer work when he constructed several programcontrolled calculators. In this essay, his developments between 1936 and 1945 are described. In Section 1, the basic concepts of Zuse’s machines, such as binary and floating-point arithmetic, are explained. These principles have been implemented in Zuse’s first four general purpose machines, the Z 1, Z 2, Z 3, and Z 4, which are examined in Section 2. Section 3 concludes with some remarks on Zuse’s achievements. 1 The Basic Concepts of Zuse’s Machines At the beginning of the 1930s, Konrad Zuse studied civil engineering at the Technical University Berlin-Charlottenburg. As a student he had to perform many extensive calculations in the field of statics. These calculations initiated Zuse’s thoughts on the automation of such computations. His goal was the development of a machine that could perform complex, schematic calculations automatically and that was adapted to the particular needs of engineers and scientists. One of the most important properties of his machine is the fact that it is program-controlled. The advantage is that a program has to be written only once and can then be used for an arbitrary amount of instances of the same problem. This situation applied to Zuse’s calculations that he had to do at university: the same type of calculations repeated again and again, but each time with different numbers. Obviously, the concept of a machine that is controlled by a program has a great impact on the error rate of such computations. As soon as the program has been specified correctly and the machine works reliable, no further errors can occur, while there is the permanent jeopardy of a mistake when a human – even a very skilled one – performs the same calculation again and again. [5] Zuse realized that even very complicated numerical computations could be expressed by such a program if they fulfilled two preconditions: 1. It must be possible to reduce them to basic operations. 2. They must be expanded explicitly. If these conditions are satisfied, a program can be constructed in the following way: all variables (input, temporary, and output) that appear are enumerated. In todays terminology, these numbers correspond with the addresses of the registers [9]. Then, the program consists of a sequence of equations; each equation consists of the addresses of one or two operands, an operation and an address for the (temporary or final) result. The hardware that can deal with these programs consists of the following components: 1. An arithmetic logic unit (ALU) that performs the actual calculations. After the operands have been set and the basic operation has been selected, the ALU performs the operation automatically. 1Zuse used the term “Rechenplan” [calculation plan] instead of “program”.