Teacher blog: Mr Lee - computer science visit

10th October 2017

Colussus at Bletchley ParkDISKovering the story of computing at Bletchley Park

A group of Year 11 students visited Bletchley Park on 3rd October 2017 to discover how algorithms and computers were used in World War Two and how technology has developed over time.

Tunny and Colossus
The first exhibit was Tunny and Colossus.  The need for such computers came about during World War Two when, in the midst of war, the German’s were using the Lorenz machine to encrypt communication with their soldiers.  The German’s transmitted messages using Morse code and the teleprinter alphabet.  The Lorenz machine had various settings for determining how to encrypt messages, in fact, there were 10151 different possible settings on the machine, so Hitler thought it was invincible.  It was perhaps for this reason, why the German’s began to make mistakes when communicating with their soldiers.

Bill Tutte, a British codebreaker and mathematician, began to notice some of these mistakes and was able to discover how the Lorenz machine worked despite the fact that he didn’t have a physical machine, just some punched tape.  He was able to use this to develop an algorithm for detecting the settings of the Lorenz machine.  This algorithm could be executed on a machine called Colossus.

The second machine, Tunny, was able to use the Lorenz settings from Colossus to decrypt German messages.  It is believed that this innovation by Tutte shortened the war by 18 months.

Students were able to discover how logical XOR operations could be applied to a character and a random character to encrypt some text., which links well with the computer science curriculum.

Harwell Dekatron
The second exhibit was the Harwell Dekatron.  This computer is based on the von Neumann architecture, which students have learnt about in class.  It has the same components including memory (RAM), a CPU, registers and an ALU.  It was particularly illuminating to see how this computer actually executed a computer program by observing how the instructions and data are loaded into memory before the results of processing are stored in a register called the accumulator.  This is essentially how a modern day computer works.  It was also particularly noteworthy that the computer’s memory was stored as denary numbers which meant the computer needed a translator to convert these into binary to be executed by the CPU.

The Harwell Dekatron was built in 1950 and was used in the calculations required to build a nuclear power station.  It is the world’s oldest, original computer and is remarkably similar to modern computers in function.  However, technological trends have led to the miniaturisation of components and an exponential increase in memory and processor speeds.

Developments in computer technology
Students were able to gain an understanding of how computer technology has developed over time, including: advances in memory technology, advances in processing technology, particularly the use of the transistor and developments of Internet-based technology.

Practical programming and problem solving
Finally, the students were able to engage with some practical-programming tasks. They started to experiment with algorithms which tried to address the Turing test for intelligence. This test is essentially a way of asking a computer questions and judging whether the answers could have been provided by a computer, rather than a machine. Students were able to see how this problem could be potentially approached with an algorithm, albeit quite primitive, it did allow them to begin thinking about how it could be solved.

The final task involved finding out how to program a BBC micro computer from the 1980s.  Although students were given the base code for a game of snake, many were asking insightful questions and were able to adapt the program to include more features such as obstacles and opponent snakes.

Students found the day enjoyable and were able to see how some of the theory they have learnt is applied in real algorithms and computer systems.  The tour guide found the students to be particularly well-engaged and enthusiastic. 

Mr Lee
Computer Science