Z3 (computer)
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Zuse Z3 replica on display at Deutsches Museum in Munich

Konrad Zuse's Z3 was the world's first working programmable, fully automatic computing machine; whose attributes, with the addition of conditional branching, have often been the ones used as criteria in defining a computer. The Z3 was built with 2,000 relays. (A request for funding for an electronic successor was denied as "strategically unimportant".) It had a clock frequency of ~5–10 Hz, and a word length of 22 bits.^[1] Calculations on the computer were performed in full binary floating point arithmetic. Z3 read programs off a punched film.

The machine was completed in 1941. On May 12, 1941, it was successfully presented to an audience of scientists of the DVL (Deutsche Versuchsanstalt für Luftfahrt, i.e. German Laboratory for Aviation), in Berlin.^[2] The original Z3 was destroyed in 1943 during an Allied bombardment of Berlin. A fully functioning replica was built in the 1960s by the originator's company Zuse KG and is on permanent display in the Deutsches Museum. The Z3 was used by the Nazi government's German Aircraft Research Institute to perform statistical analyses of wing flutter in aircraft design^[3].

How the Z3 relates to other work

Unlike the first non-programmable mechanical computer built by Wilhelm Schickard in 1623, the Z3 of 1941 was program-controlled.

The success of Zuse's Z3 is often attributed to its use of the simple binary system. This was invented roughly three centuries earlier by Gottfried Leibniz; Boole later used it to develop his Boolean algebra. In 1937, Claude Shannon of MIT introduced the idea of mapping Boolean algebra onto electronic relays in a seminal work on digital circuit design (see also Z1). Nevertheless, Zuse (who did not know Shannon's work) was the one who put the ideas together and made it work on the program-controlled Z3.

The first design of a program-controlled computer was Charles Babbage's Analytical Engine in the 1830s.

Britain's 10 codebreaking Colossus computers^[4] were the first electronic digital computers. They used thermionic valves (vacuum tubes) and binary representation of numbers. Programming was by means of re-plugging patch panels and setting switches. This development was kept secret for many decades which led to claims of "firsts" in computing that later turned out to be incorrect.

The ENIAC was completed after the war. It used thermionic valves (vacuum tubes) to implement switches, and decimal representation for numbers. Until 1948 programming was, as for Colossus, by patch leads and switches.

The Z3 stored its program on an external tape, thus for reprogramming no rewiring was necessary.

The Manchester Baby of 1948 and the EDSAC of 1949 were the world's first computers with internally stored programs, implementing a concept frequently attributed to a 1945 paper of John von Neumann and colleagues. The concept had actually been mentioned earlier by Konrad Zuse himself, in a 1936 patent application (which was rejected).

Relation to the concept of a universal Turing machine

It was possible to construct loops on the Z3, but there was no conditional jump instruction. Nevertheless, the Z3 was Turing-complete – the way of implementing a universal Turing machine on the Z3 was shown in 1998 by Raúl Rojas.^[5][6] He proposes that the tape program would have to be long enough to execute every possible path through both sides of every branch. It would compute all possible answers, but the unneeded results are canceled out. Rojas concludes, "We can therefore say that, from an abstract theoretical perspective, the computing model of the Z3 is equivalent to the computing model of today's computers. From a practical perspective, and in the way the Z3 was really programmed, it was not equivalent to modern computers."

From a pragmatic point of view, however, the Z3 provided a quite practical instruction set for the typical engineering applications of the 1940s – Zuse was a civil engineer who only started to build his computers to facilitate his work in his main profession.

See also

• Manchester Small-Scale Experimental Machine
• Manchester Mark I
• Manchester Mark II
• IBM SSEC

Notes and references

External links

• Z3 page at the Technical University of Berlin
• The Life and Work of Konrad Zuse
• Konrad Zuse?s Legacy: The Architecture of the Z1 and Z3 (PDF)
• How to Make Zuse's Z3 a Universal Computer Raúl Rojas
• Raúl Rojas, The Zuse Computers in RESURRECTION The Bulletin of the Computer Conservation Society ISSN 0958-7403 Number 37 Spring 2006