Z3

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This article is about the Z3 pioneering computer from 1941. For the BMW automobile, see BMW Z3.

Konrad Zuse's Z3 was the first working programmable, fully automatic 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, 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.

The machine was completed in 1941 (on May 12 that year, it was successfully presented to an audience of scientists in Berlin). The original Z3 was destroyed in 1944 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. In 1998 the Z3 was proven to be Turing-complete.

1 How the Z3 relates to other work
2 Relation to the concept of a universal Turing machine
3 See also
4 Notes and references
5 External links

[edit] How the Z3 relates to other work

Unlike the first non-programmable 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 Difference Engine in the mid 1800s. A working model was not made in his lifetime, presumably because its decimal design was much more complicated than the binary Z3. In 1991 a difference engine was completed, using Babbage's original plans, and functioned well. If Babbage's friend Ada Lovelace was the first theoretical programmer, writing programs for a machine that did not exist, then Zuse was the first practical programmer.

The ENIAC was completed 5 years after the Z3. ENIAC used vacuum tubes to implement switches, Z3 used relays (a request for funding for an electronic successor was denied as "strategically unimportant"). ENIAC was decimal, Z3 was binary. Until 1948, to program ENIAC actually meant to rewire it; while the Z3 read programs off a tape (actually a punched film). Today's computers are based on transistors instead of tubes or relays; their basic architecture, however, is much more similar to Z3's than to ENIAC's. Z3 needed an external tape to store its program. 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. A patent application of Konrad Zuse, however, mentioned this concept almost a decade earlier in 1936, although the patent was rejected.

*Defining characteristics of five first operative digital computers*
Computer	Shown working	Binary	Electronic	Programmable	Turing complete
Zuse Z3	May 1941	Yes	No	By punched film stock	Yes (1998)
Atanasoff-Berry Computer	Summer 1941	Yes	Yes	No	No
Colossus	December 1943 / January 1944	Yes	Yes	Partially, by rewiring	No
Harvard Mark I/IBM ASCC	1944	No	No	By punched paper tape	No
ENIAC	1944	No	Yes	Partially, by rewiring	Yes
ENIAC	1948	No	Yes	By Function Table ROM	Yes

[edit] 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 (although it would have been rather straightforward to insert one). Nevertheless, there is a way of implementing a universal Turing machine on a Z3 (assuming unlimited storage and zero crashing probability), as was shown in 1998.

From a pragmatic point of view, however, it is much more relevant that 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—and that in many pioneering ways it was quite similar to modern computers.