The COLOSSUS, Z4, and Mark 1 : A short history and description

by

Robert Apple

Cmptr Arch & Operating Systems MCT*611*XP40 < instructor name removed > May 12, 2007

Colossus, Z4 and Mark 1 2

COLOSSUS, Z4 and Mark 1 Computers

The invention of the electronic is a relatively new development, happening within the last 100 years. It has an interesting history. During the World War II years (about

1938 – 1945), independent researchers developed three different computer systems: the Colossus

(United Kingdom), Z4 (Germany), and Mark 1 (United States). This paper will briefly describe the forces driving the creation of those systems and some of the technical details of each.

To begin this discussion, a basic understanding of vacuum tubes, and relays or switches is necessary. A vacuum tube relies on a principle called the ‘Edison Effect’. When electrons are flowing through a filament inside a glass tube that contains no air, not only will the filament light up producing the ‘light bulb’, it is also possible to mount a metal plate inside of that tube which allows some of the electrons to jump from the filament to that metal plate (Maxfield & Brown

[1], n.d.). Building on this fact, the English physicist John Ambrose Fleming developed a two- filament vacuum tube that was called a diode (Maxfield & Brown [1]). The diode can be used as an on/off switch: if electricity is passing through the filament, the electrons passing from the filament to the metal plate inside could be considered an on/off switch depending on how the machine using the tube is configured.

A relay is a switch formed from coiling wire around a metal bar held in place by a small spring. When current is passed through the coil, the metal bar moves. As the electrical current is stopped, the metal bar is returned to its original position by the spring. Depending on the configuration of the machine, the position of the metal bar could be considered an on/off switch

(Maxfield & Brown [4], n.d.).

Switches and vacuum tubes, because of their general size at the time, were cumbersome in comparison with the digital circuits used in modern computers. This fact, as will be discussed

Colossus, Z4 and Mark 1 3 below, contributed to the extremely large and heavy computer configurations. However, they were all important tools used in the initial stages of computer development (Maxfield & Brown

[2], n.d.).

During World War II, the German military forces adopted a means of encrypting their radio communications. This encryption method became know to Allied groups as “Enigma”

(Copeland, 2000). The Polish Cipher Bureau cracked this encryption routine in 1932, and in July

1939 the Poles shared their information with the British (Copeland & Proudfoot, 2004). Because the British now knew how to decipher the messages, they were armed with knowledge of

German intelligence; however, they had one problem -- there were so many messages that it was difficult to decipher them in a timely manner.

Besides the Enigma code, the Germans created another cipher “…that was employed for their ultra-top-secret communications” which became known as Fish (Maxfield & Brown [3], n.d.). In 1943, a man named Alan Turing, along with some of his associates, started construction on an electronic machine that they dubbed the Colossus. This machine was programmable through switch manipulation and wire changes. It proved successful in helping the British decipher German communications (Maxfield & Brown [3]). Ultimately the code was cracked and Germany no longer had as many secrets during the war. “F. H. Hinsley, official history of the GC&CS, has estimated that the war in Europe was shortened by at least two years as a result of the signals intelligence operation carried out at Bletchley Park, in which Colossus played a major role" (Copeland, 2000).

According to Copeland (2000), Colossus had the following characteristics:

Colossus, Z4 and Mark 1 4

Colossus I contained approximately 1600 vacuum tubes and each of the subsequent

machines approximately 2400 vacuum tubes. Like the smaller ABC, Colossus lacked

two important features of modern computers. First it had no internally stored programs.

To set it up for a new task the operator had to alter the machine’s physical wiring, using

plugs and switches. Second, Colossus was not a general-purpose machine, being

designed for a specific cryptanalytic task involving counting the Boolean operations.

Copeland (2000) further states: “The first fully functioning electronic digital computer was Colossus (1943), used by the Bletchley Park cryptanalysts from 1944…Colossus stopped running in 1960 (during its later years, it was used extensively for training).” The length of use for this computer indicates it was successful enough to remain many years after the war.

Another computer was simultaneously invented in Germany by . He was responsible for the , , , and Z4 machines ("Z4", n.d.). Zuse was a mechanical engineer who was frustrated with the time it took to make calculations with the old pencil and slide rule method. As a result, he built what became the Z1 in his parent’s living room in 1938 in .

This computer, unlike the Colossus, relied on relays. Later when he constructed the subsequent models, the Z3 utilized the binary number system and could perform floating-point calculations, and though he considered using vacuum tubes for this machine, he decided against it (“Z4”).

Zuse wasn't supported for his work as the German government felt they were close to winning the war (Bellis [1], n.d.). There were also casualties: in 1944, the original Z3 was destroyed. However, Zuse was working on the general-purpose relay computer, the Z4, at this time (Maxfield & Brown [2], n.d.).

Colossus, Z4 and Mark 1 5

The Z4 was a frontrunner of many modern computers in that it was the “…first electronic, fully programmable digital computer based on a binary floating point numbers and switching system" (Bellis [1], n.d.). As mentioned earlier, many of these computers were cumbersome in size. The Z4, for example, could perform approximately 11 multiplications per second, but used 4000 watts of power and weighed approximately 1000 kg (“Z4”, n.d.).

The instruction set utilized for this machine was conceived in 1942 and included instructions to move data from memory cells into registers, copy the contents of registers to memory, perform basic arithmetic operations between registers; dyadic operations such as (x) squared, (x) to the 10th power, (x) * (/1/5) could also be performed. The Z4 also allowed basic comparison instructions and conventional branch instructions (“Z4”, n.d.).

Zues is responsible for creating the first algorithmic programming language in 1946 called Plankalkül. It utilized several of the aspects of current programming languages including arrays and records, right hand assignment, and array subscripts (“Z4”, n.d.).

It was estimated that the Z4 performed approximately 100 different projects which totaled about 100,000 instructions, indicating its versatility (“Z4”, n.d.). Truly the Z4 has made a significant contribution to today’s computer technology.

America also had its computer systems. Howard Aiken and Grace Hooper were responsible for the design of the Mark series of computers at Harvard University. This all began with the Mark 1 in 1944 (Bellis [2], n.d.). This computer was the first large-scale automatic digital computer in the United States, and was created at IBM, eventually shipped to Harvard in early 1944 ("Harvard Mark 1", n.d.).

The Mark 1 utilized punched tape and tape readers to receive input but did not possess any conditional branching instructions. As a result, program looping could only be

Colossus, Z4 and Mark 1 6 accomplished by “…joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a loop)” (“Harvard Mark 1”, n.d.). Fortunately, the data was separated from the instruction.

The Mark 1 could store up to 72 numbers, each containing up to 23 decimal digits in length; could do three additions or subtractions in a single second, multiplications in 3 seconds, but other operations like division, logarithm or trigonometric functions took longer (“Harvard

Mark 1”, n.d.). By today’s standards, the machine was extremely slow, but considering there aren’t many people who can perform repetitive multiplications of 23 decimal digit long numbers in 3 seconds, it was a computational marvel for its time.

Each of the computers mentioned in this document was large and cumbersome. Because of the secret nature of the Colossus and its use in World War II, the Prime Minister of Brittan ordered it destroyed. ("What Was the First," 2005). Consequently, it is difficult to get dimensions of what the thing actually had. However, records do exist for the Z4 and Mark 1 machines. The Z4, as mentioned above, weighed approximately 1000 kg. Pictures indicate it would fit in a normal sized large room. The Mark 1, however, was the largest of the three. It was 51 feet long, weighted 5 tons, incorporated 650,000 parts (Cruz, 2004), was eight feet high and two feet deep, and used at least 500 miles of wire ("Harvard Mark 1", n.d.).

The Colossus, Z4 and Mark 1 have all played roles in history and were created during the

WWII years by independent researchers. They were early pioneers of the computer invention explosion that still continues today.

Colossus, Z4 and Mark 1 7

References

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http://www.alanturing.net/turing_archive/pages/Reference%20Articles/

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Copeland, J., & Proudfoot, D. (2004, May). Alan Turing, codebreaker and computer pioneer.

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Colossus, Z4 and Mark 1 8

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