The Worlds First Digital Electronic Computer
Below are some pictures with a narrative beside each one. Click on an image below to see a larger version of the picture. When viewing a larger picture, clicking "Next" allows you to look at the larger pictures one at a time.
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There were two entirely different types of Nazi messages that were decoded at Bletchley Park during World War II: Enigma and Lorenz. This photo shows the more widely-known Nazi Enigma encoding/decoding unit. It was used to encrypt and decrypt Morse Code messages. It was portable, using only a few flashlight (torch) batteries to power the lettered lights in the center. The operator used the letter keys to enter one letter and then he wrote down which letter was lit up. The code wheels at the top and the patch panel on the front of the machine established the letter scrambling for that month, week or day (depending on how often the code was changed). After he had entered each letter of the message and written down the corresponding encoded letters, the operator sent the resulting message via radio, keying each letter using Morse Code. British operators at short wave receivers at a variety of sites around Britain intercepted the radio messages and meticulously wrote down the meaningless letters of the Nazi messages. The messages were all sent to Bletchley Park via several different mediums (telegraph, teleprinter, motorcycle courier, and mail). |
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Bletchley Park had collected a broad mixture of clever mathematicians, scientists, engineers and German language experts, plus chess and puzzle experts. They developed this machine to help decrypt the Enigma messages. Many people contributed to the design of the machine but Alan Turing provided much of the theory. They called the machine the Bombe. It did not include any electronics. It was entirely electromechanical. |
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This reconstructed Bombe is fully functional. The electrical panel that is swung open (on the right in the picture) includes the input patch panels and relays. On the left are the mechanical gears and wheels, which are powered by the large electric motor at the base of the machine. There is an automated oil distribution system for the gears, so on the floor is an oil pan to collect the dripping oil. |
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The machine sequentially tried every letter until it detected a match. When a match was found the machine stopped and the operator read the decrypting code letters from this large bank of wheels on the other side of the machine. |
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Even more spectacularly, the amazing people at Bletchley Park developed methods and machines to decrypt Nazi Lorenz teleprinter messages. These were not tactical messages but strategic messages between Hitler's staff and the major military command centers. To decrypt these important messages Bletchley Park ended up developing the world's first digital electronic computer. The Lorenz encoding/decoding machine was a box full of coding wheels that was attached to a conventional teleprinter. The British did not capture a Lorenz machine until after the war ended. The experts at Bletchley Park figured out how it worked without ever seeing a real one. The teleprinter (like a Teletype or Telex machine) had a keyboard similar to a typewriter, a paper tape punch for recording messages, a paper tape reader for sending messages typed off-line and a printer for displaying messages. |
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The Nazi messages produced on a Lorenz machine were far more challenging for the Bletchley Park code breakers. The Bombe designed for Enigma messages was not of much use. They designed an electromechanical machine specifically for the Lorenz code, but it was far too slow to decode the growing volume of Lorenz messages. So Bletchley Park adopted the electronic machine that was designed and built at the telephone research laboratory, and called it Colossus. This picture shows half of the computer, including the tape reader at the other end. There is a second set of floor-to-ceiling equipment racks behind the ones seen here. |
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The man in the center of this picture, Tony Sale, led the project to build this replica of the Second World War Colossus. Part of his motive was to prove that the British built an electronic computer before the Americans. He proved his point eloquently with thorough archival research followed by actual building of a replica as identical as possible to the machine that went into operation in early 1944. The first electronic computer in the US, also a war-time project, did not begin operating until nearly a year later (at the University of Pennsylvania in Philadelphia; it was later commercialized as Univac). The lady at the far end was one of thousands of teenage girls who helped with code breaking at Bletchley Park during the Second World War. Now she is a Bletchley Park tour guide. The visitor on the left, who is responding appreciatively to Tony Sale's talk, is Richard. The racks of equipment seen here are primarily the input and output stations. The code breakers specified the logical operations that should be performed for the next computer run and the operators entered them on switches and dials. The output was on a panel of lights that indicated the statistical likelihood that the computer had identified the correct encryption code. |
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The primary component of electronics in the 1940s was of course vacuum tubes, called valves by the British. I count 87 tubes on the panel shown in this picture. For you younger people who haven't seen or used tube-based electronics, compared to a transistor, a tube is large (three to six inches high and a inch or two in diameter), a tube gets very hot, a tube uses a lot of power (at a high voltage) and a tube has a filament and so they burn out like an incandescent light bulb. During the war they never turned a Colossus computer off (it was busy decrypting Nazi messages 24 hours per day). The designers realized that filaments almost always burn out when the tube is turned on or turned off. They seldom fail while operating at a constant temperature. |
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This picture shows a portion of the logical processing part of the computer. The orange glow of the hot filament (heater, as tube designers refer to it) is visible in many of the tubes in this photo. There are about 2500 vacuum tubes in Colossus. To put that in modern perspective, the chip that formats keystrokes in your keyboard for your computer probably has about 2500 transistors, not counting its memory. It is probably fair to say that there is more computing capacity inside your keyboard, or mouse, or TV remote control than in Colossus. Colossus consumes about 5000 watts of electricity. During the war one would guess that people liked working in a room with Colossus during the winter with so much heat radiating from the machine. All of the vacuum tubes used in the Colossus replica are between 40 and 70 years old. They have been accumulated from discarded old electronic equipment and donated personal stashes of old tubes. They say a tube in the replica Colossus burns out about once per week. |
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This picture shows the wiring on the back side of one of equipment racks. Countless hundreds of hours were devoted by volunteers to building this Colossus replica. The tour guide said the individual panels were made at home by a volunteer and then they were brought to Bletchley Park to be wired together. |
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Once the set-up parameters were entered into the control switches, Colossus was run by the paper tape image of the intercepted encrypted Nazi message. The paper tape has a sprocket hole and five data bit positions. Five bits allows a maximum of 32 different characters. It could only encrypt letters of the alphabet. Because of the encryption methods they used, I believe the messages could not use numbers or punctuation. Numbers could only be sent by spelling the words. |
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Nazi encrypted teleprinter messages tended to be lengthy, typically several thousand characters. Since the British were intercepting the messages as transmitted from far away by radio, receiving errors were common. So for important Nazi communications links (for example, from the western front field headquarters to Hitler's headquarters), messages were recorded at multiple intercept sites. When multiple versions of the same message reached Bletchley Park, great care was devoted to merging them into a paper tape that most likely was accurate. The tape was spliced into a continuous loop. The tape loop was put on these wheels, which were then adjusted for the length of the loop. There are two paper tape readers. While Colossus is operating upon one Nazi message tape, the tape for the next message can be put into the idle tape handler. In this photo the tape on the right is idle (the punched holes can be seen) while the tape on the left is a blur because it is moving very fast. |
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The paper tape moves between the light source and the electronic sensors. The speed of the tape establishes the speed of the computer. The signal derived from the sprocket hole is the clock pulse that drives the logic circuits of the entire computer. The Colossus tape reader was typically run at 5000 characters per second. For computer users today, 5 kHz may seem to be a slow computer execution speed, but that left only 200 microseconds for the logic to fully process each Nazi message character. The tape moves at the rate of 41.7 feet per second -- that's a high speed tape reader! And it was built that fast in 1943! War time memories say that as an experiment the tape reader was sped up to 9000 character per second. The computer logic worked fine at that speed but the tape broke and threw tape around the room at a rate of 50 miles per hour. So it was normally run at about 5000 characters per second to reduce the risk of paper cuts to the people in the room. |
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This picture shows the light sensors and circuitry of the dual tape readers. I find both the early 1940s original Colossus and the replica to be remarkable. It is amazing what they were able to create in 1943 with little prior experience of digital electronics. Some could claim that Colossus was not a full fledged computer, but I would counter that all of the early computers lacked portions of a modern computer. It took another 10 to 15 years for a computer as we know it today to be technologically possible. In particular, it took a long time for a practical random access memory technology to become available for program storage. It seems that Colossus had data storage so that the logic could see the current and four previous message characters. That's 25 bits of memory. The documentation I've seen on the Colossus memory isn't fully clear to me, but it seems that each memory bit used two thyratron vacuum tubes. It also seems that thyratron shift registers (memory) were also used to sequence each possible code wheel setting into the decryption logic. Colossus did not have a full-fledged arithmetic processor; only a binary half-adder was needed for decryption. Colossus did not have conditional program sequencing (if-then-else). Colossus did not have a way to store a program, that was the responsibility of the human operator and cryptologist. Colossus was a remarkable accomplishment. It was probably 20 times larger than any previously built electronic equipment. That led to electronic general purpose computers after the war, as well as large electronic telephone switching systems. Colossus showed the feasibility of high speed paper tape as a data storage medium, which led the way in later years to high speed magnetic storage which we still use every day, our hard drives. About ten Colossus computers were built before the end of the Second World War. All of them were eventually destroyed and their existence was kept secret for decades. However, some of the individuals familiar with the technology were after the war involved in computer developments in academia and industry in Britain and to a lesser extent in the US. If you have further interest, I found the book "Colossus, Bletchley Park's Greatest Secret" by Paul Gannon to be very good. |
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