The Life and Work of Konrad Zuse (by Horst Zuse)

Part 4: Konrad Zuse's Z1 and Z3 Computers
The Z2 Computer
Unsatisfied with the reliability of the binary switching metal sheets used in the Z1, Konrad Zuse next constructed the Z2 computer. The Z2 used the same type of mechanical memory as the Z1, but he used 800 old relays from phone companies to construct the arithmetic and control units. The Z2’s arithmetic unit consisted of a 16-bit fixed-point engine, because he wanted to test the reliability of relays for arithmetic calculations. Unfortunately, photos and plans of the Z2 were destroyed by allied air raids during the war. However, the Z2 served its purpose, because it convinced my father that relays were indeed reliable, and he subsequently built his Z3 computer completely out of relays (600 for the arithmetic unit and 1,800 for the memory and control units).

The Z3 Computer (1939-1941)
Helped by friends and with some small support from the government, Konrad Zuse constructed his Z3 machine from 1939 to 1941 in the Methfesselstraße 7 in Berlin-Kreuzberg. He wanted to use the Z3 to demonstrate that it was possible to build a reliable, freely programmable computer based on a binary floating point number and switching system, which could be used for very complicated arithmetic calculations. For reliability reasons he used relays for the entire machine.

The original design of the Z3 drawn by Konrad Zuse in 1939
Fig.24. The original design of the Z3
drawn by Konrad Zuse in 1939.
The Z3 that was rebuilt in 1960/61
Fig.25. The Z3 that was rebuilt by
Konrad Zuse in 1960/61.

The original design of the Z3 is illustrated in Fig.24. Unfortunately no photos of the original Z3 exist, because all documents and photographs were destroyed by allied air raids during the Second World War.

Konrad Zuse rebuilt the Z3 at his Zuse KG(3) company between 1960 and 1961 (Fig.25)  in order to demonstrate the performance of this machine to justify his patents and to show the world his creation (and also to demonstrate the machine for advertising purposes). Like the original machine, the rebuilt Z3 is completely constructed from relays. The Z3's memory (64 words, each comprising 22 bits) is seen on the left-hand side of Fig.25. The console is at the front, while the binary floating point arithmetic unit appears on the right-hand side. The Z3 is about five meters long, two meters high, and 80cm wide.

(3)The Zuse KG (where "KG" means a special type of company in the form of a limited partnership) was founded in 1949 in Neukirchen (Kreis Hünfeld). This is about 120km north of Frankfurt.

In 1957, the Zuse KG was moved to Bad Hersfeld, which lies 15km north of Neukirchen. This move was prompted by the lack of space for rooms and the cramped production facilities.

Konrad Zuse with the rebuilt Z3 in 1961
Fig.26. Konrad Zuse with the rebuilt Z3 in 1961. The memory is
on the left (note the "Z" logo Z of the Zuse KG company). The arithmetic unit with the stepwise relays are on the right, and
the console with punch tape reader is on the front left.
A page from Konrad Zuse's diary (May 12, 1941)
Fig.27. A page from Konrad
Zuse’s diary from May 12, 1941, when he presented the working
Z3 to scientists in Berlin.
It is now undisputed that the Z3 was the first reliable, freely programmable, working computer in the world based on a binary floating-point number and switching system. In 1941, the Z3 contained almost all of the features of a modern computer as defined by John von Neumann and his colleagues in 1946 [BURK46]. The only exception was the ability to store the program in the memory together with the data. Konrad Zuse did not implement this feature in the Z3, because his 64-word memory was too small to support this mode of operation. Due to the fact that he wanted to calculate thousands of instructions in a meaningful order, he only used the memory to store values or numbers.
A block diagram of the Z3
Fig.28. A block diagram of the Z3.
The rebuilt Z3
Fig.29. The rebuilt Z3 (1961).
The block structure of the Z3 is very similar to a modern computer. The Z3 consisted of separate units, such as a punch tape reader, control unit, floating-point arithmetic unit, and input/output devices. With respect to this theme, Burks et al. [BURK46] wrote as late as 1946, "In as much as the completed device will be a general-purpose computing machine it should contain main organs relating to arithmetic, memory-storage, control and connection with the human operator. It is intended that the machine be fully automatic in character, i.e. independent of the human operator after the computation starts."

It is important to note that the Z3 fully met Burks’ requirements. Also, the Z3 supported a special operating mode, because the Lu instruction stopped the program and activated the input device. The human operator could check, among other things, the contents of the Registers R1 and R2 in the arithmetic unit, he or she could perform intermediate calculations using the Registers R1 and R2, then the operator could continue running the program.

Previous Section    Return to Index    Next Section


Copyright & Contact Info

Return to EPE Online Home Page