Starting with computers, invented by Konrad Zuse in 1938-1945.
The Zuse Z1–Z4 machines were a progression of early German programmable computing systems designed by Konrad Zuse between the late 1930s and 1940s. They evolved from a mostly mechanical prototype (Z1) into a practical electromechanical computing system (Z3/Z4). Their I/O, architecture, and use cases are pretty different from modern computers, so it helps to break them down by machine.
Big picture: what were they used for?
Across all four systems, the goal was engineering and scientific computation. Especially aerodynamics (aircraft wing calculations), structural engineering and general numerical mathematics (floating-point arithmetic). They were not “general computers” like today’s PCs in the software sense. They were programmable numeric calculators used mainly for solving equations, iterative numerical methods or matrix and structural calculations. The Z3 and Z4 were actually used for real engineering work, especially war-related aerospace research.
Z1 (1938) — Mechanical experimental computer. Z1 - what it was: a fully mechanical binary floating-point computer, uilt from metal plates and mechanical logic, it was very experimental and unreliable.
Input was punched 35mm film tape, encoded instructions, keyboard input was possible but limited. Output was a mechanical display system, and basic numeric output (not interactive like modern systems). Use? Mostly a proof of concept. Demonstrated that binary + programmable logic could work mechanically. Real-world usage? Basically none; it was too unreliable for practical computation.
Z2 (1939) — Hybrid prototype
Z2 - what it was: a hybrid system, using mechanical memory (from Z1), w/ relay-based logic unit. Input was punched film tape (program instructions), output was simple mechanical/indicator output. Use was a small-scale testing machine and a bridge between Z1 and fully functional Z3. Usage? Engineering experiments only. No known production use.
Z3 (1941) — First working programmable computer
Z3 - what it was: the first fully working programmable automatic computer w/ ~2,600 electromechanical relays and binary floating-point arithmetic. Input (important) was punched celluloid film tape, program instructions stored externally, manual numeric input via keyboard, and initial values entered by operator. Output was light-lamp display panels (results shown as numbers), sometimes printed or manually recorded. How it was used - Aerodynamics and engineering calculations, example: wing flutter and structural load problems. It could run long computations unattended. Limitations: no stored-program memory, no true branching (limited control flow) anx program = physical punched tape sequence. Still: this was the first time a machine could: run a fully automatic numeric program without human intervention during execution.
Z4 (1945–1950) — First “commercial” Zuse computer. Z4 - what it was: an improved version of Z3, most advanced Zuse machine and the first Zuse system actually used for ongoing external work. Input (more advanced I/O): punched film tape (program input), decimal floating-point input via keyboard, program preparation unit (helped create punch tapes). Output: typewriter output (Mercedes typewriter system), printed numeric results, also mechanical indicators in some configurations. Real usage (important): after WWII, the Z4 was installed at ETH Zurich (1950–1955) where it was used for engineering mathematics, structural analysis, numerical simulations and research computations. This is the first Zuse machine that was reliably used in an academic/industrial environment, essentially a “service computer” for engineers.
What “I/O” really meant in Zuse machines
Unlike modern computers, I/O was very physical: input methods - punched film tape (program = instructions), keyboard (manual numeric entry), external preparation devices (Z4 improved this). Output methods - lamp panels (binary/decimal display), typewriters (Z4) and sometimes manual transcription by operators. There were no screens, no interactive UI and no storage drives. Everything was batch-style computation.
Summary in one line
Z1 → mechanical proof of concept
Z2 → hybrid experiment
Z3 → first real working programmable computer (engineering calculator)
Z4 → first practical deployed computing service machine (used at ETH Zurich)
