Z4 (computer) - Construction

Construction

The Z4 was very similar to the Z3 in its design but was significantly enhanced in a number of respects. The memory consisted of 32 bit rather than 22 bit floating point words. A special unit called the Planfertigungsteil (program construction unit), which punched the program tapes made programming and correcting programs for the machine much easier by the use of symbolic operations and memory cells. Numbers were entered and output as decimal floating point even though the internal working was in binary. The machine had a large repertoire of instructions including square root, MAX, MIN and sign. Conditional tests included tests for infinity. When delivered to ETH Zurich the machine had a conditional branch facility added and could print on a Mercedes typewriter. There were two program tapes where the second could be used to hold a subroutine (originally six were planned).

In 1944 Zuse was working on the Z4 with around two dozen people, including several women. Some engineers who worked at the telecommunications facility of the OKW also worked for Zuse as a secondary occupation. To prevent it from falling into the hands of the Soviets, the Z4 was evacuated from Berlin in February 1945 and transported to Göttingen. The Z4 was completed in Göttingen in a facility of the Aerodynamische Versuchsanstalt (AVA, Aerodynamic Research Institute), which was headed by Albert Betz. But when it was presented to scientists of the AVA the roar of the approaching front could already be heard, so the computer was transported with a truck of the Wehrmacht to Hinterstein in Bad Hindelang, where Konrad Zuse met Wernher von Braun.