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The Z4 was the world's first commercial digital computer, designed by German engineer Konrad Zuse and built by his company Zuse Apparatebau between 1942 and 1945. The Z4 was Zuse's final target for the Z3 design, and like it, was an electromechanical machine.
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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 sine. 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. 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.
Usage after World War II
In 1949, the Swiss mathematician Eduard Stiefel, after coming back from a stay in the USA where he inspected American computers, visited Zuse and the Z4. When he formulated a differential equation for Zuse, who immediately programmed the Z4 to solve it, Stiefel decided to acquire the computer for his newly founded Institute for Applied Mathematics at the ETH Zurich. It was delivered to ETH Zurich in September 1950.
In 1954 Prof. Wolfgang Haack tried to obtain the Z4 for the Technical University of Berlin, but it was instead transferred to the Institut Franco-Allemand des Recherches de St. Louis (ISL, Franco-German Institute of Research) in France, where it was in use until 1959, under its technical head Hubert Schardin. Today, the Z4 is on display in the Deutsches Museum in Munich. The Z4 inspired the ETH to build its own computer (mainly by Ambros Speiser and Eduard Stiefel), which was called ERMETH, an acronym for German: Elektronische Rechenmaschine ETH ("Electronic Computing Machine ETH").
In 1950/1951, the Z4 was the only working digital computer in continental Europe (the British had several, probably as many as eleven), and the second digital computer in the world to be sold, beating the Ferranti Mark 1 by five months and the UNIVAC I by ten months, but in turn being beaten by the BINAC (although that never worked at the customer's site). Other computers, all numbered with a leading Z, were built by Zuse and his company. Notable are the Z11, which was sold to the optics industry and to universities, and the Z22.
In 1955 the Z4 was sold to the French-German Research Institute of Saint-Louis (Institut franco-allemand de recherches de Saint-Louis) in Saint-Louis, close to Basel, and in 1960 transferred to the German Museum in Munich.
The Z4 was used for calculations for work on the Grande Dixence Dam.