In , Tony Sale and his team began the ambitious task of rebuilding a working Colossus. They succeeded and in it was tested in the global Colossus Cipher Challenge. Once again Colossus was able to crack the Lorenz code in 3. Much work has still to be done to complete perhaps the world's most exciting computing exhibit, but already Colossus is viewable by the public as never before and is set to inspire future generations of engineers and computer scientists.
Colossus was the first of the electronic digital machines with programmability, albeit limited in modern terms. The notion of a computer as a general purpose machine - that is, as more than a calculator devoted to solving difficult but specific problems - would not become prominent for several years. Colossus was preceded by several computers, many of them being a first in some category. Colossus, however, was the first that was digital, programmable, and electronic.
The first fully programmable digital electronic computer capable of running a stored program was still some way off - the Manchester Small Scale Experimental Machine. The use to which the Colossi were put was of the highest secrecy, and Colossus itself was highly secret, and remained so for many years after the War. In recent years, however, both the UK and US governments have declassified and released papers giving more information about Colossus.
During WW2, the Germans relied mostly on the Enigma machine to encode messages. Enigma traffic was first broken before the war in Poland, and continued to be broken throughout much of the war at Bletchley. The German Army High Command, however, did not rely on Enigma, but on a more complex system based on encoded teleprinter traffic using a machine developed by the Lorenz company.
The Lorenz machine worked with teleprinter punched hole paper tape shown above 32 symbol baudot code. The message was encoded by combining the original with a sequence of obscuring characters using modulo 2 addition exclusive NOR in boolean terms.
At the receiving end the message was decoded by once again adding the same sequence of obscuring characters. Had the sequence of obscuring characters been truly random it would have been impossible to break the code, but luckily for the code breakers, the sequence was generated by rotating mechanical wheels and was a repeating pseudorandom sequence — if this sequence could be unravelled the code could be broken.
Working at Bletchley, Brigadier John Tiltman and the Cambridge graduate Bill Tutte exploited mistakes made by German radio operators and began to reconstruct the pseudorandom sequence and discover how the Lorenz encoding machine worked.
This was completed in and the Post Office Research Labs at Dollis Hill were asked to build a machine to replicate the operation of a Lorenz machine at this time they had not even seen a picture of a Lorenz machine. The problem was the time taken to work out the correct settings. This was a manual and laborious task that often took weeks or even months for a single message, so long in fact that by the time it was decoded the information was useless. This involved having two loops of paper tape. The first contained the message to be decoded and the second contained the repeating pseudorandom sequence.
The idea was that each time the loop of tape containing the message was fed through the machine, the second tape was moved on by one position. In this way each possible setting was tested and a score recorded for each. TRE at Malvern were approached to develop a machine to implement the idea. In this way, a thyratron can store one bit of information electronically. Once the pattern of ones and zeros on the wheels were known, these could be stored in the thyratron rings and used to find the correct settings for several messages.
The Colossus machine was driven by the tape reader which scanned punch holes in a tape representing the cipher text of a message. The punch holes were converted by a photoelectric reader into a sequence of pulses which were then sent to the arithmetic and logic circuits of Colossus for processing. The tape also contained a series of "sprocket holes" which were used for the timing of the processing.
Each pulse from a sprocket hole was essentially one tick of the clock that ran Colossus. At each tick pulses from the tape and from the thyratron rings are sent to delta circuits which calculate the delta of each stream of bits. The delta circuits contain capacitors which delay a pulse long enough that it can be added modulo 2 to the next input pulse.
This process calculates the delta of each input stream because it will output a one if two consecutive bits are different and a zero when they are the same. As described in the page on the double delta attack, the wheel settings that produced the most zeros from the above process were likely to be correct. Colossus contained counters to keep track of each time the combination of the two input delta streams in the logic circuits produced a zero.
An operator of the machine would manually set a threshold which, when it was exceeded by the count of zeros for given wheel settings, would cause the wheel settings and the number of zeros for those settings to be printed out. In , at the age of 25, Fournier d'Albe took a job writing book abstracts for The Electrician magazine and then Physical Society.
This work exposed him to a world of cutting-edge scientific discoveries and exceptional thinkers. During his lifetime, he would befriend H. Wells, W. Campbell-Swinton , and the magician and spiritualist Harry Houdini. In , Fournier d'Albe decided to pursue a career in physics. Through his impeccable contacts, he secured a post as an assistant lecturer at the University of Birmingham under the renowned physicist Oliver Lodge. Lodge recommended that Fournier d'Albe focus his doctoral research on selenium.
Selenium's unusual photoelectric properties first surfaced in experiments at the Telegraph Construction and Maintenance Co. The resistance was highest when the sample was enclosed in a dark box.
Removing the box's cover caused the conductivity to jump. Selenium named for the Greek goddess of the moon, Selene would soon become known as a wonder material, and several inventors attempted to exploit it.
Most famously, Alexander Graham Bell used the metal in his photophone of , a telecommunications device that relied on modulated light to transmit a wireless signal. Conceptually, Noiszewski's invention was remarkably similar to Fournier d'Albe's exploring optophone, which came later. Given his extensive research into selenium, Fournier d'Albe almost certainly would have known about the electroftalm. That may explain why he was so willing to drop the exploring optophone in favor of developing the reading optophone.
Although Fournier d'Albe excelled in many things, he was not an engineer. And so his reading optophone, while based on sound theory, took eight years and much support to move from prototype to product. The reading optophone worked by scanning a tiny portion of the page at a time. A small rotating disk that spun at 30 rpm would break up an artificial light source into a line of five beams, each with a different frequency.
When the beams were reflected onto a selenium cell, the fluctuations in light intensity would be mirrored by variations in the conductivity of the selenium.
To turn the changes in conductivity into an audible signal, Fournier d'Albe used a telephone receiver from S. Brown Ltd that could detect fluctuations in current down to a millionth of an ampere. The notes C, D, F, G, and B represented the frequencies of the five light beams and would mix to create different chords. So the poor listener had to interpret the sounds generated by the space around each letter rather than the sounds generated by the letters themselves.
With such a system, Fournier d'Albe estimated it would take around 8 hours to learn the audible alphabet and 10 to 20 lessons to discern basic words. Adding a second selenium cell, called a balancing cell, enabled the machine to read black text. The white signals canceled each other out so that only the black signal was magnified. Other design modifications included a magnifying lens for reading different sizes of text, as well as a worm thread that let the user slow the reading from 5 seconds per line to as long as 5 minutes.
Even the most experienced reader never achieved the fastest speed, as I'll discuss in a bit. A final improvement held the book or newspaper stationary on a frame over the reading mechanism, and the reading head, or tracer, pivoted on an axis to read the line.
On the white sounding optophone, the user had to keep carefully repositioning the book—a tricky task for someone who was blind. Once again, Fournier d'Albe was overreaching. There was certainly a need for a tool like the optophone, considering the hundreds of thousands of World War I servicemen who had been blinded by gas or shells. And yet this innovative and potentially life-changing machine failed to find a foothold in the market. By the time Fournier d'Albe died in , only a tiny number of optophones perhaps as few as a dozen had been sold.
What can account for the optophone's commercial failure? Fournier d'Albe's reputation might have contributed to the problem. Like many of his generation, he was an ardent spiritualist. The invisible world of electromagnetic waves and the discovery of electrons were tearing up the scientific rule book.
In a photo, Margaret Hogan top used the black sounding optophone to read a book. The black optophone also allowed the user to control the scanning speed, and it didn't require the text to be manually repositioned.
Against that backdrop, it was not a huge leap to believe that a human soul might also be stored somehow within invisible energy forces. He even assigned them a weight: 50 milligrams. His book prompted a backlash from the establishment.
For the optophone to succeed, Fournier d'Albe knew he needed the backing of the National Institute for the Blind, a powerful association that in the United Kingdom acted as the unofficial gatekeeper to his intended audience. Pearson had been a celebrated newspaper magnate at the start of the century, but as he slowly lost his sight due to glaucoma, he transferred his energy to supporting people who were blind. Pearson had invested heavily in providing Braille resources throughout the country, so a new machine that threatened to make Braille obsolete was never going to receive his backing.
By the inventor's account, everything went off without a hitch, and he used the machine to accurately read a random sample from the daily newspaper at a rate of four words per minute. But when Pearson and the committee released their opinion in an open letter to the London Times a few days later, they could not have been more scathing. They concluded that the machine was little more than an interesting scientific toy—hard to learn and far too slow for any practical use.
Compounding the NIB's lack of support was the optophone's price. When the black sounding optophone was released three years later, the price had tripled. Too expensive for the average household, it was still affordable by medical institutions. Without the backing of the NIB, however, this was unlikely to happen. In a twist of fate, the National Institute for the Blind was finally pressured into buying a single black sounding optophone in after King George V and Queen Mary saw one at an exhibition and gave it a glowing review.
One of the few optophones still known to exist is in the collection of the charity Blind Veterans UK , which was founded by the man who so opposed the technology—Arthur Pearson.
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