Zuse Z3 1941 — computing with relays (3D)
About this app
Konrad Zuse's Z3, the first working program-controlled computer: memory, arithmetic unit, console and punched film. A relay in close-up switches, then a floating-point addition runs bit by bit: align exponents, add mantissas, normalise — with your own numbers.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What the Z3 was
Konrad Zuse demonstrated the Z3 on 12 May 1941 in Berlin. It is regarded as the first working, program-controlled, fully automatic digital computer. Instead of valves, about 2,600 relays did the work: electric switches flipped by an electromagnet, pulled in 1, released 0. The Z3 computed with binary floating-point numbers of 22 bits, had 64 memory words and ran at about 5 cycles per second. The program came from punched cinema film. The original was destroyed in 1943; a 1961 replica is at the Deutsches Museum.
What the app shows
The app shows its own reconstruction of the machine with memory, arithmetic unit, control, console, lamp panel and film reader. A small program reads two numbers, adds them and displays the result. In the relay view you see coil, iron core, armature, spring and contact in section. The calculation shows a floating-point addition in Z3 format: every bit is a relay with a lamp, grouped into sign, exponent and mantissa.
What you can try
Switch the current through the coil on and off and watch the armature close the contact. Enter two numbers of your own and go through the six steps of the addition one by one: compare exponents, shift the mantissa, add digit by digit with carry, normalise. The example 10 + 0.1 shows why floating-point numbers are not exact. In the Data panel you place the Z3 next to Harvard Mark I, ENIAC and the Manchester Baby.
Frequently asked questions
- How did the Zuse Z3 work?
- The Z3 consisted of about 2,600 electromechanical relays. Each relay stored or processed one bit. It computed with 22-bit binary floating-point numbers, read its program from punched cinema film and displayed results in decimal on a lamp panel. An addition took three cycles, a multiplication about three seconds.
- Was the Z3 the first computer in the world?
- In 1941 the Z3 ran as the first working, program-controlled, fully automatic digital computer. ENIAC followed in 1945/46 and was electronic and much faster. Neither was stored-program. Which machine counts as the first computer therefore depends on the definition.
- What is a floating-point number in the Z3?
- A number made of sign, exponent and mantissa, similar to 1.25 · 2³. The Z3 used 1 bit for the sign, 7 bits for the exponent and 14 bits for the mantissa. The leading 1 of the mantissa was not stored. That is why numbers like 0.1 can only be represented approximately.
- Is the machine in the app the original or the museum replica?
- Neither. The app shows its own simplified reconstruction. The original was destroyed in 1943; the Deutsches Museum shows a replica from 1961.
Subject: Physics experiments (Deutsches Museum)
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