Digital programmable computer

The digital programmable computer emerged because the mathematical foundations for automatic calculation had been laid by Turing and others in the 1930s—and a German civil engineer working in isolation would build the first working implementation while the rest of the world remained unaware.

Konrad Zuse (1910-1995) was a civil engineer frustrated by tedious structural calculations. He began designing automatic calculators in his parents' Berlin living room in the late 1930s, working in complete isolation from computing developments elsewhere. His Z1 (1938) and Z2 (1940) were experimental machines that demonstrated key concepts.

On May 12, 1941, Zuse presented the Z3 to scientists at the Deutsche Versuchsanstalt fur Luftfahrt (German Laboratory for Aviation) in Berlin. The Z3 was built with 2,600 electromechanical relays, implementing a 22-bit word length operating at 5-10 Hz. Program code was stored on punched film.

The Z3 used a binary system with floating-point arithmetic—remarkably sophisticated for its era. Numbers were represented with one sign bit, seven exponent bits, and fourteen mantissa bits. The machine stored 64 words and could perform addition, subtraction, multiplication, division, and square root extraction.

The Z3 was demonstrated in 1998 to be Turing-complete in principle, though it lacked conditional branching and achieved completeness only through speculative computation of all possible outcomes. It was the world's first working programmable, fully automatic digital computer.

The Z3 was used for aerodynamic calculations before being destroyed in a British bombing raid on Berlin in late 1943. Zuse's work remained unknown outside Germany during and after the war, while Colossus (1943, Britain) and ENIAC (1945, America) received attention as independent developments.

Zuse built a fully functioning Z3 replica in 1961 through his company, Zuse KG; it now resides permanently at the Deutsches Museum in Munich. In 1999, Zuse received the Computer History Museum Fellow Award 'for his invention of the first program-controlled, electromechanical, digital computer and the first high-level programming language, Plankalkul.'

The Z3 represents the adjacent possible becoming manifest: Turing's theoretical foundations, relay technology from telephone switching, and one engineer's determination converging in wartime Berlin. That the first digital programmable computer emerged in Nazi Germany, built in a living room, and was destroyed by Allied bombs before its significance could propagate—this underscores how contingent technological history can be.