The Life and Work of Konrad Zuse (by Horst Zuse)
Part 7 (continued): The Zuse KG
The Z25 Computer
The development of the Z25 computer commenced in 1961. The goal was a small and cheap machine that would be suitable for many different applications.

A computer center containing Z25 machines
Fig.84. A computer center containing a number of Z25 machines at the Thyssen AG (a steel company) in 1964. The Z25 was used as a process computer. In the Thyssen AG, Z25 computers controlled the transportation of ores on more than 15km of conveyer belts.

The first four Z25s were delivered in 1964, and by 1969 the Zuse KG had delivered 102 machines. However, in 1964 the Zuse KG got into severe financial trouble because of a production problem with the Z25. A transistor needed a special method to be soldered, but this was not known by the head of production. The result was that production had to be stopped for eight weeks, but the company still had to pay the employees' salary. This was the end of Konrad Zuses ownership of the Zuse KG.

The Zuse KG in Bad Hersfeld in 1964
Fig.85 (Above). The Zuse KG in Bad Hersfeld in 1964. At this time the company had approximately 1,200 employees.

The advertising slogan of the Zuse KG from 1960

Fig.86 (Right). The advertising slogan of the
Zuse KG from 1960: Zuse - Your Partner.
As was mentioned above, beginning in 1962 the Zuse KG got deeper and deeper into financial difficulties. There were a number of reasons for this as follows:

Bullet

 There was no financial support of the computing industry by the government.
Bullet There was increasing competition from IBM and other computer manufactures.
Bullet The patent situation of Konrad Zuses computers had not been solved at this time. The decision on these patents was not made until 1967 (the story of Konrad Zuses patents can be found in Rojas [ROJA98]).
Bullet Partially mismanagement.
Bullet Too fast growing of the company.
Bullet Software unbundling. Software development cost the Zuse KG more and more, but the customer did not want to pay money for this.
Bullet No other sources of income, because computers were the only production subject of the Zuse KG.
Bullet Renting of computers instead of selling them. Banks did not give credit for this.
Starting in 1962, the Zuse KG implemented much effort to control production in factories using process computers. This was very interesting to a steel company called Rheinstahl, and the Zuse KG was bought by Rheinstahl in 1964. In 1965, BBC (Brown Boveri and Cie), which produced power plants, electric equipments, and so forth bought the Zuse KG from Rheinstahl. Finally, in 1967, the Zuse KG was bought completely by the Siemens AG. In 1969, the Zuse KG logo was deleted by the Siemens AG and Konrad Zuse left the Zuse KG.
Computers sold in Germany by the Zuse KG from 1949-1969

A Zuse KG advertisment from 1961
Fig.87 (Left). A map showing computers sold in Germany by the Zuse KG from 1949-1969. The Zuse KG sold about 250 computers from 1949 to 1969 of a value of ca. 100 Million DM. Fig.88 (Right). A Zuse KG advertisment from 1961.
The following table gives an overview of the most important computers produced by Konrad Zuse and the Zuse KG from 1936-1969 (note that the "Pieces" column refers to the number of units created). We also mention some machines that were not discussed above, but we do not list every special machine that was produced by the Zuse KG. However, in [ZUSE98] every machine of the Zuse KG is described and illustrated with a picture, and a real-time simulation of the Z3 is also presented.

Year(s)

 Name Pieces Comments
1936-1938 Z1 1 First machine in the world with: a binary floating point processor, binary logic, parallel working devices, freely programmable, separation of memory, control unit, arithmetic unit, input/output devices. Bistable mechanical building blocks, 64 words (each containing 22 bits). Not a stored program computer. Worked unreliably.
1938-1939 Z2 1 Fixed point arithmetic, 800 relays, 16 bits binary fixed point processor, mechanical memory, test model for relays. Not a stored program computer .Worked reliably.
1940-1941 Z3 1 First working computer in the world with: binary logic, powerful binary floating point processor, arithmetic exception handling, 2400 relays, 64 words (each containing 22 bits), separation of memory, control unit, arithmetic unit, input/output devices. Not a stored program computer.
1942-1945 Z4 1 Successor of the Z3, but with a mechanical memory of 64 words (each containing 32 bits), 2200 relays, binary floating point processor, arithmetic exception handling, extended in 1949 for the ETH-Zürich from 1950-1955: conditional branch, call of subprograms (second punch tape reader), MERCEDES output device. Not a stored program computer.
1942 S1 1 Special computer for measuring the surface of wings of airplanes, hardware wired program, 600 relays, binary principle, 12 bits word length, destroyed 1944. Not a stored program computer.
1944 S2 1 Improved version of the S1, automatic scanning of wings with about 100 clock gauges, hardware wired programs, destroyed in 1945. Probably the first process computer in the world. Not a stored program computer
1950-1952 Z5 1 Mandated by Leitz / Wetzlar (for optical calculations), extension of the Z4 with many punch tape readers and a punch writer, six times faster than the Z4, binary principle, floating point arithmetic, 32 bit words, biggest relay computer in Germany, first commercial computer in Germany, 300,000 DM. Not a stored program computer.
1951-1955 Z7 30 Calculating punches, mandated by Remington Rand, 30 pieces, called Remington M9. Not a stored program computer.
1955 Z11 38 Used for consolidation of farming, hardware wired programs, later freely programmable, floating point processor, easily to use by pressing buttons, 120,000 DM in 1960. Not a stored program computer.
1957 Z22 50 First electronic computer of the Zuse KG, 38 bit words, fixed point arithmetic, minimal principle, magnetic drum containing 8,192 words, first stored program computer of the Zuse KG, very successful, 180,000 DM.
1961 Z23 87 First transistor computer, same logic as the Z22, three times faster than Z22, 40 bit words, very successful. Stored program computer.
1963 Z25 105 Small and very flexible computer, 18 bit words, process control in companies, many peripheral devices, 98,000 DM. Stored program computer.
1961 Z31 7 Parallel development to the Z23, designed for commercial applications (such as banks), decimal arithmetic unit, too expensive and too large, flop for the Zuse KG. Stored program computer.
1958 Z64 85 Drawing machine with high accuracy (1/20 mm), controlled by punch tapes, used for graphical representation and in the optical industry.
1965 Z43 >100 Modern transistor computer, TTL logic. Stored program computer.
Table 1: A list of the computers produced by Konrad Zuse and the Zuse KG from 1936-1969. The rebuilt Z1 stands in the Deutsche Technik Museum in Berlin-Kreuzberg. The rebuilt Z3 and the original Z4 are on display in the Deutsche Museum München. The Z11 computer can be visited in the Heinz Nixdorf MuseumsForum in Paderborn, which is the greatest computer museum in the world. The Z11 also can be visited in the Deutsche Technik Museum in Berlin, where a Z23 and Z64 can also be seen. The Z22 is on display in the Deutsche Museum München and in the Stadt- und Kreisgeschichtliche Museum in Hünfeld, where the city Hünfeld shows some of Konrad Zuses computers, including the Z22, Z23, Z25, and Z64. In Hoyerswerda, where Konrad Zuse lived from 1924-1928, a Z22, which is still working, will be installed in the living house of his parents. In September 1999, a Z23 will be shipped to Silicon Valley (Boston Computer Museum).
From my perspective, the story of the Zuse KG is a fascinating one. From 1949 to 1969, the Zuse KG produced about 250 computers with a value of 100 Million DM. Although the Zuse KG had orders of more than 25 Million DM in 1964, and the expected gross revenues were close to 40 Million DM, it was impossible for Konrad Zuse to keep the Zuse KG as his own company. From its founding in a back yard in the small village of Neukirchen (Kreis Hünfeld) in 1949, the Zuse KG grew to be a very creative computer company until 1969 (owned and controlled until 1964 by Konrad Zuse).
The Zuse KG started with five employees in Neukirchen in 1949.

The Zuse KG grew up to be a modern computer company in Bad Hersfeld
Fig.89 (Left). The Zuse KG started with five employees in Neukirchen in 1949. Fig.90 (Right). The Zuse KG grew up to be a modern computer company in Bad Hersfeld (15 km north of Neukirchen) with about 1200 employees in 1964. Konrad Zuses office was on the top of the building (red color).
From my point of view, Konrad Zuse was not a collapsed entrepreneur. Konrad Zuse and his company was years ahead of his time in designing computers, producing computers, drawing machines controlled by computers, and ideas related to computers.

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