A Swiss retired technician appears to have kept the manual for the Zuse Z4 in his archive. For a long time it was thought that there was no manual for the oldest computer still in its original condition, but it has now been rediscovered.
The manual for the Zuse Z4 was kept by René Boesch, who was a researcher at the Institute for Aircraft Statics and Aircraft Construction at ETH Zurich in the 1950s. The Z4 carried out about a hundred calculation projects there between 1950 and 1955, including the course of missiles, aircraft wings, vibrations and dives.
The ETH, or the Eidgenössische Technische Hochschule Zürich, had the Z4 on loan and eventually returned this computer, built in 1945, to Zuse KG. The extensive system is now in the Deutsches Museum in Munich.
The manual was provided by Boesch to Herbert Bruderer, who also worked at ETH Zurich and writes about the find for the Association of Computing Machinery. The documents have been digitized and published online.
The Z4 was the successor to the Z1, Z2 and Z3 and was the first computer to be commercially available. The systems were designed by the German computer scientist Konrad Zuse. Work on the Z4 started in 1942 and the computer was ready a few days before the end of World War II. The system consists of 2500 relays and mechanical memory. The Z4 worked with 32bit floating point “words” and operated at a frequency of 40Hz. Programming was done with a so-called Planfertigungsteil for punch cards. The system took about 400ms to add and 3 seconds to multiply.