Zuse Z3

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Replica of the Zuse Z3 in the Deutsches Museum in Munich

The Z3 was the world's first functional digital computer and was built in 1941 by Konrad Zuse in cooperation with Helmut Schreyer in Berlin . The Z3 was implemented in electromagnetic relay technology with 600 relays for the arithmetic unit and 1400 relays for the storage unit.

Like the Z1, the Z3 used the binary floating point arithmetic introduced into computer technology by Konrad Zuse . In contrast to the design and use of the ENIAC , the design of the Z3 did not meet the later definition of a powerful computer and it was never used that way. It was only in 1998 that it was found out that, from a purely theoretical point of view, it nevertheless had this property through clever use of complex detours. In Germany in particular, the Z3 is considered to be the world's first functional universal computer. It was destroyed in a bombing raid in 1944.


Berlin memorial plaque for the Zuse Z3 in Methfesselstrasse 7 in Berlin-Kreuzberg

The development of the Z3 was preceded by the development of the fully mechanical Z1 and the transition model Z2 . The German Research Institute for Aviation looked at the Z2 and gave Zuse 25,000 Reichsmarks so that he could build the Z3. On May 12, 1941, the Z3 was finally presented to a group of scientists (including Alfred Teichmann and Curt Schmieden ). When Zuse was briefly drafted into the war in 1941, he wrote to a friend: "Others leave the family behind, I leave the Z3." ( Konrad Zuse : Famous alumni of the Technical University of Berlin )

The original Z3 calculating machine was destroyed by bombing raids on Berlin in 1944 during World War II. It was a tragic moment for Zuse as he no longer had any proof that there really was a working Z3. A functional replica, which was made in 1962 by Zuse KG for exhibition purposes, is in the Deutsches Museum in Munich. At the former location, on the ruins of the house on Methfesselstrasse in Berlin's Kreuzberg district , a plaque commemorates Zuse's workplace. Since Konrad Zuse's 100th birthday on June 22, 2010, a replica of the Z3 has been exhibited in the Konrad Zuse Museum in Hünfeld .



In addition to the fact that it was the first fully functional programmable digital computer, the Z3 contained many features of modern computers:

The Z1 also had almost all of the features listed above, but did not attract as much attention because its arithmetic unit did not work very reliably due to its mechanical structure. In general, the structure of Z1 and Z3 are very similar to one another, which is especially true for the arithmetic unit.


Electromagnetic memory built into the Z3, Z5, Z11 type computer

The Z3 consisted of

  • a relay - floating point arithmetic unit (600 relays) for addition, subtraction, multiplication, division, square root, decimal-dual and dual-decimal conversion. The arithmetic unit has two registers R1 and R2.
  • a relay memory (1400 relays) with a storage capacity of 64 words, 22 bits each (1 sign bit , 7 bit exponent, 14 bit mantissa )
  • a punched tape reader for film strips to read in programs (but not data)
  • 30,000 cables
  • a keyboard with lamp field for input and output of numbers and manual control of calculations.

The computer looked like a wall unit and filled an entire room. It weighed about a ton.


The Z3 is a clocked machine. The timing is done by an electric motor that drives a timing roller. This is a drum that rotates approx. 5.3 times per second and controls the individual relay groups during one rotation. The speed of rotation of the drum corresponds to the processing rate of modern main processors , which means that this computer has a speed of 5.3 Hz. The main memory of the Z3 is 200 bytes. The Z3 has the following machine commands :

command description Duration (cycles)
Pr z Load memory cell z into register R1 / R2 1
Ps z Write R1 to memory cell z 0-1
La Addition: R1 ← R1 + R2 3
Ls Subtraction: R1 ← R1 - R2 4-5
Lm Multiplication: R1 ← R1 × R2 16
Li Division: R1 ← R1 / R2 18th
Lw Square root: R1 ← √ (R1) 20th
Lu Read in decimal number in R1 / R2 9-41
Ld Output R1 as a binary number 9-41

Numerical data must be entered using the keyboard, i.e. numbers cannot be coded on the punched tape. All operations except memory access (Pr and Ps) can be carried out directly via the keyboard. The punched tape can only contain commands, each command being coded with 8 bits. The exact coding on punched tape can be found in the article Opcode .

The Z3 knows no jump commands , but with the help of skilful use of the finite computational accuracy it is powerful , as Raúl Rojas showed in 1998. However, this result is only of theoretical importance, since programs with jump instructions have to be laboriously transformed and the program runtime increases.

Arithmetic unit

Every arithmetic operation of the Z3 is based on the addition of two natural numbers. This basic operation of addition is calculated by XOR (XOR (x, y), CARRY (x, y)), where CARRY (x, y) is the carry function, e.g. B. CARRY (0011011, 1010110) = 0111100.

  • Two floating point numbers are added by calculating the difference between the exponents , then matching the mantissa of a number accordingly, and finally adding the mantissas.
  • A subtraction corresponds to an addition in which the two's complement of the second mantissa is used, and the carry is omitted.
  • A multiplication corresponds to adding the exponents and then multiplying the mantissas. The mantissas are multiplied by iterative addition: 1011 × 0101 = 1011 + 10110 × 010 = 1011 + 101100 × 01 = 110111 + 1011000 × 0 = 110111.
  • A division corresponds to a multiplication, but the exponents are subtracted and an iterative subtraction is used to divide the mantissas.
  • The algorithm for pulling a root is implemented by an iterative division (see patent specification).

In general, the arithmetic unit consists of two parts, a work for calculating with exponents and a work for calculating with mantissas. For commands in which iterative methods are used (Lm, Li, Lw, Lu, Ld), a sequencer is used to control individual parts of the calculator. This roughly corresponds to modern microprograms.


Several test programs and a program for the calculation of a complex matrix were written for the Z3 , which was used according to a solution by Hans Georg Küssner to calculate critical flutter frequencies in aircraft. The use of the computer was not classified as urgent at the time , so that routine operation never came about.

Comparison with ENIAC

The ENIAC (in the foreground Betty Snyder , in the background Glen Beck )

In the USA and large parts of the world, the ENIAC , built in 1944, is regarded as the first computer, which can be explained by the fact that the two computers have different properties and different criteria are used to define the term computer.

The Z3 was the first digital computer and at the same time the first binary, programmable and powerful Turing. However, in contrast to ENIAC, which used tubes, it was not electronic (a funding application by Helmut Schreyer for an electronic successor model was rejected by the Reich government as not essential to the war effort); In addition, the Turing power is only made possible thanks to a trick not foreseen by the designer. The ENIAC was the fifth digital computer in history and the first to meet the criteria electronic, programmable and powerful at the same time. It worked with the decimal system, which means it was not a binary computer like the Z3 and like all modern computers. In Germany, due to its older age and its binary way of working, with which all computers still work today, the Z3 is generally assigned this title, whereas the aspect of hardware design is less important.

The historical preference for the ENIAC may also be due to the fact that it received much more attention in the USA after the Second World War than the Z3, which was destroyed in a bomb attack.

Computer model country Installation Floating point
Binary Electronically Programmable Mighty Turing
Zuse Z3 Germany May 1941 Yes Yes No Yes, using punched tape Yes, without any practical use
Atanasoff-Berry computer United States Summer 1941 No Yes Yes No No
Colossus UK 1943 No Yes Yes Partly, by rewiring No
Mark I. United States 1944 No No No Yes, using punched tape Yes
Zuse Z4 Germany March 1945 Yes Yes No Yes, using punched tape Yes, without any practical use
around 1950 Yes Yes No Yes, using punched tape Yes
ENIAC United States 1946 No No Yes Partly, by rewiring Yes
1948 No No Yes Yes, using the resistor matrix Yes

Other Zuse computers (selection)

2011 Zuse Z3 replica with Finder relay


Web links

Commons : Zuse Z3  - collection of images, videos and audio files

Individual evidence

  1. Zuse 2010 p. 55.
  2. 70 years ago: America got to know the first electronic universal computer ENIAC , Heise online on February 14, 2016
  3. konrad-zuse.net
  4. a b c d e Dr. Kristina R. Zerges, S. Terp: Konrad Zuse . The father of the computer. Ed .: Press and information department of the Technical University of Berlin (=  famous alumni of the Technical University of Berlin ). omnisatz GmbH, Berlin.
  5. ^ The Z3 and Z4 by Konrad Zuse. In: German Museum. Retrieved August 6, 2020 .
  6. Pierre Kurby: 70 years of Z3: How many Zuse Z3 computers do you need to win Jeopardy? In: e-recht24.de. May 12, 2011, accessed January 8, 2018 .
  7. RAÚL ROJAS: Konrad Zuse's Legacy: The Architecture of the Z1 and Z3 . In: IEEE Annals of the History of Computing, Vol. 19, No. 2, 1997 . S. 5–16 (English, ed-thelen.org [PDF; accessed October 11, 2018]).
  8. ^ Raúl Rojas : How to make Zuse's Z3 a universal computer . In: Annals of the History of Computing . tape 20 , no. 3 . IEEE, 1998, ISSN  1058-6180 , doi : 10.1109 / 85.707574 ( PDF Scan , PDF , HTML ( Memento from August 3, 2014 in the Internet Archive )).
  9. Hans Dieter Hellige (Ed.): Stories of Computer Science. Visions, paradigms, leitmotifs. Springer, Berlin 2004, ISBN 3-540-00217-0 .
  10. Zuse 2010 p. 57.
  11. Hans-Willy Hohn : Cognitive structures and control problems in research. Nuclear physics and computer science in comparison . Frankfurt am Main / New York 1998, ISBN 3-593-36102-7 ( online (PDF; 1.3 MB) page 148 - writings of the Max Planck Institute for Social Research Cologne, volume 36).