Konrad Zuse. Biography. Contributions. Zuse-Companies. Z3r. Tour-Zuse-Computer. Z23 Crosses Altlantic. Early Computers. Neumann vs Konrad Zuse. Impressum and Contact. Professor Dr.-Ing. habil.
Horst Zuse


A most economical small desk-size computer.

 Word length 18 bit, 38 basic instructions, up to 1024 index strorage cells Maximum working speed 7100 operations/s.

 Ferrite core working store for extension up to 16384 words Ferrite core fixed store for extension up to 4096 words.

 Auxiliary magnetic drum store holding 17664 words.

 Magnetic tapes with a working speed of 100 000 characters/s Input and output via punched tape, punched cards, line printer Connection of data sampling systems for process control

 Several ZUSE Z 25 can be coupled together.

 The central unit occupies very little space.

The extraordinarily wide range of extension facilities, both as regards the stores and the peripheral equipment, assure the ZUSE Z 25 a widespread field of applications. The low purchase price of the central unit allows to be augmented economically to form multiple systems with, depending on the nature of the problem, may processes identicval or different programs in true simultaneous operation.

For Science and Engineering

Small-scale computer for use in institutes, low cost and small s ize.

In conjunction with the film translator ZUSE Z 84, the electronic planimeter ZUSE Z 80 and the "Graphomat" ZUSE Z 64, it can be used to achieve complete automation in surveying. With appropriately increased storage capacity it makes an ideal technical computer.

In the Commercial Field

High internal data processing speed obtained with the aid of special instructions for double length arithmetic. High-speed data input by punched-tape reader for 300 or 1000 characters/s, high-speed data output by tape punch for 150 characters/s and line printer working at 5 lines/s.

Quick sorting with high-speed magnetic tapes. The writing or reading speed is 100 000 characters/s.

Owing to the low price of the central unit, true simultaneous operation of the system can be obtained by using several central units type Z 25 coupled together.

For process Control

Automatic sampling of measurands and data of a process, as well as transfer to the central unit over Jong distances by the flexible data sampling system.

Satellite systems can be formed by coupling several ZUSE Z 25 together. The interchangeability of all components of the system, including the central unit Z 25, assures maximum possible reliability, which is absolutely essential in the field of process control.

Central unit

Length of word 18 bit, word time 140 µs

Representation of numerical data: binary (corresponding to appr.5 decimals/word)

Instruction word

2'conditional bit

1 bit address modification

5 bit function part

10 digit address (unmodified)

38 instructions, including double-length instructions.

Wired multiplication and division.

Transfer of instructions from store and execution in 1 word time.

32 interruption channels for breaking into programme.

Input and output channels for direct data transfer between several ZUSE Z 25 at internal machine speed.

Ferrite core working store, max.capacity 16384 words.

Extension stages: 256/1024 an 4 x 4096 words.

Ferrite core fixed store holding 2048 or 4096 words.

High-capacity Store

Magnetic drum store for 17664 words.

Average access time per block 5 ms.

Magnetic tape unit with a reading or writing speed of 100 000 characters/s.

Capacity per 170 m tape (1/2 in.) appr.1 million words.

Data input

Punched-tape reader for 10, 300 or 1000 characters/s Punched-card reader for 12 000 cards/h

Input of analogue values from data sampling systems.

Data output

Tape punch for 10 or 150 characters/s

Teleprinter for 10 characters/s

High-Speed printer for 100 characters/s

Line printer for 5 lines/s

Output of analogue values via data distribution systems Analogus on-line and off-line output via automatic

plottingtable ZUSE Z 64 Graphomat

Output register for digital values for control of relays.


Control desk with 18-bit indicator for register and storage cells Regulated power supply

Printed circuit cards

Hinged chassis which simplify maintenance.


Areas of application

A general purpose computer for application in all areas of science, technology, process control, administration and commercial application. It was possible to extend the Z25 with additional memory, magnetic cylinder and magnetic tape and other peripheral devices. Complex systems for process control could be realized through coupling of several Z25 and devices for data input. Direct output of calculation results to the Graphomat Z64 possible.

Z25 (German)

Zuse-Computer (German)


Goto the Z31 ...

Name of Machine
Z25 (from 1963)
Transistors in the MHZ range.
Ca. 294.000 Hertz
Arithmetic Unit
Floating point, 18 bit or 36 bit word length.
Average calculation Speed
500 operations in a second.
Almost all available input devices.
Almost all available output devices. Interrupt channels, connextion with the Graphomat Z90 was possible.
Word Length
18 bit oir 36 bit
Ferrir core until 16392 words, drums with 17664 words.
Power Consumption
400 KG
Area of Application
110 in Germany, 10 in foreign contries (2 in Moskau)
Zuse-Computer (English)
Zuse-Computer (German)
Konrad Zuses Work on a DVD
Functional Z25 in the Arithmeum in Bonn.