Why Build Colossus? (Bill Tutte) - Computerphile | Summary and Q&A

September 14, 2018
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Why Build Colossus? (Bill Tutte) - Computerphile


The video discusses the development of Colossus, a special-purpose computer used during World War II, and the transition from electromechanical to electronic computing.

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Questions & Answers

Q: Why was Colossus necessary for code-breaking during World War II?

Colossus was needed because the amount of counting required in code-breaking was enormous, and humans were incapable of handling it all. The computer was used to search for patterns and count the occurrences of zeros.

Q: Why did early attempts at electromechanical machines fail to meet the requirements?

Electromechanical machines were not fast enough for the code-breaking task. Even with attempts to speed them up, they would often malfunction and take days to complete the counting needed. This led to the decision to shift to electronic computing.

Q: How did thermionic valves play a role in reliable electronic computing?

Initially, valves were seen as unreliable due to frequent blowouts. However, Tommy Flowers suggested that with careful handling, such as quickly bringing up the heaters of the cathodes, valve blowouts could be minimized. This approach, combined with lowering the voltage slowly at the end of the day, made valves more reliable for electronic computing.

Q: Did Colossus have limitations in its code-breaking capabilities?

While Colossus was highly effective, there were occasional challenges. If a message had an equal number of zeros and ones, it disrupted the statistical bias that Colossus utilized. In these cases, further analysis and adjustments were required.

Summary & Key Takeaways

  • Colossus was built because the counting required in code-breaking during World War II was too massive for humans to handle alone. They needed a computer to search for patterns and count the number of zeros.

  • Initial attempts at creating electromechanical machines failed to be fast enough, leading to the realization that electronic computing was necessary.

  • The use of thermionic valves and careful handling of switching on/off helped make the valves reliable enough for electronic computing.

  • Colossus was able to discover settings and patterns on Enigma cipher wheels, but occasionally a message with equal numbers of zeros and ones caused complications.

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