Konrad Zuse und der bedingte Sprung

Abstract

This paper describes the conditional instructions retrofitted by Konrad Zuse to the instruction set of the Z4 around 1950, including the conditional jump. The instruction set upgrade for the Z4 was a request from the mathematicians of the ETH Zürich, who wanted the increased functionality mainly for numerical computations. In case that the truth value in a working register was true, the conditional jump ignored all instructions in the punched tape containing the program, one after another, until a "start" mark in the code was reached. The jump instruction was otherwise ignored. Some simple programming examples help to understand the operational semantics of the conditional instructions of the Z4.