The Z1 Mechanical Computer
Berlin, 1936. Konrad Zuse, a 26-year-old man, works away in his parents’ apartment. This civil engineer has just left his position at aircraft manufacturer Henschel, where he worked as a calculator. He has a fixed idea: to build a machine capable of automating tedious mathematical calculations. Unknowingly, he is about to write an important page in the history of computing machines.
Technical naivety works in his favor. He knows nothing of IBM’s punched cards or Charles Babbage’s designs from the previous century. Free from any influence, he rethinks the architecture of calculating machines from scratch. His first technical choice is the binary system, at a time when all existing machines operate in decimal. His machine will separate memory from the arithmetic unit, manipulate floating-point numbers, and store 64 values of 24 bits.
The heart of the Z1 rests on a surprising invention. Rather than using conventional gears, Zuse manufactures metal plates that slide within a frame. A movement in one direction symbolizes a 1, the absence of movement represents a 0. These plates, stacked and connected by vertical rods, form purely mechanical logic gates. The arithmetic unit is divided into two distinct sections: one processes exponents, the other the mantissas of floating-point numbers. Four calculation phases punctuate the execution of micro-instructions, each associated with a cardinal direction.
To program his invention, Zuse reuses 35mm film stock. He punches this film according to the precise code of eight holes per instruction line, two for the operation and six for memory addressing. His eight instructions cover elementary arithmetic operations, memory transfers, input and output of results. The Z1 can also recognize special cases such as zero value (exponent -64) or infinity (exponent 63). Dedicated circuits stop the machine in case of invalid operations.
However, the elegant mechanics clash with real-world constraints. The perfect coordination of thousands of moving parts becomes a nightmare. Completed in 1938, the Z1 never functions properly. Allied bombing in 1943 reduces the machine to ashes, but the architecture will survive in the Z3, an electromechanical relay version that Zuse builds in 1941.
Forty years later, in the 1980s, Konrad Zuse begins reconstructing his firstborn for the Deutsches Technikmuseum in Berlin. This replica, completed in 1989, benefits from modern manufacturing techniques: more compact, its twelve mechanical layers contain approximately 6,000 logic gates. Despite these refinements, the machine retains the quirks of the original and requires constant monitoring.
The Z1 is remarkably at the origin of our current computers: architecture separating computation and memory (later named “von Neumann architecture”), standardized floating-point representation, binary system. These characteristics are even more impressive when one knows that Zuse had neither electronics training nor deep knowledge of formal logic.
The scarcity of materials in pre-war Germany forced Zuse to optimize every component. This minimalist approach contrasts with contemporary American projects like ENIAC or Harvard’s Mark I, which benefited from considerable budgets and large teams.
While the Z1 does not constitute a universal computer in the strict sense defined by Turing—it notably lacks conditional branch instructions—it nevertheless marks a breakthrough in the evolution of calculating machines. Its binary architecture and modular design remain the foundations of modern computing. It remains an anomaly, the almost solitary work of a visionary who, through his ignorance of established conventions, reinvented the art of mechanical calculation in the 20th century.