Were he still alive today, Alan Turing would be celebrating his 100th birthday. To mark the occasion, and Alan Turing Year 2012, two Dutch software engineers created a Turing machine completely out of Lego.
A mathematician and cryptanalyst, Turing is widely regarded as the father of computer science, particularly for devising the Turing machine, a simple device that could simulate the logic of any computer algorithm.
The hypothetical Turing machine consists of a device that can modify a strip of tape according to an input table of rules – an action which illustrates the basic functions of a CPU.
Turing proved that these machines could be capable of performing any conceivable mathematical computation that could be represented as an algorithm. To this day, Turing machines are central to the study of computation as the hypothetical device helps computer scientists to understand the limits of mechanical computation.
Alan Turing Year
To mark his centenary, 2012 has been deemed Alan Turing Year and events will run year-long, coordinated by the Turing Centenary Advisory Committee (TCAC) working with staff from the University of Manchester, Cambridge University and Bletchley Park, Buckinghamshire.
Countries around the world are participating in Alan Turing Year, and this Lego-based contribution comes from the Netherlands.
Software engineers Jeroen van den Bos and Davy Landman built the Lego Turing machine for a Turing exhibition in Centrum Wiskunde & Informatica (CWI), Amsterdam – the national research centre for mathematics and computer science in the Netherlands.
Building the Lego Turing machine
While the Turing machine is a theoretical model, Van den Bos and Landman decided to make the abstract tangible in order to better demonstrate the fundamentals of computing.
Using Lego Mindstorms NXT, this machine uses a ‘tape’ of switches and a light sensor to determine the value of a switch. If the switch is on, the sensor sees the black colour of the switch’s surface, but if it’s off, the sensor sees the white colour of the light beam. This makes it possible for the Lego Turing machine to distinguish between two states.
Add to this a rotating beam mounted above the ‘tape’, and the switches can be flipped in both directions.
Turing’s theoretical model has the luxury of infinite tape, but Van den Bos and Landman were limited to the bricks that their Lego supply allowed and so the tape was fixed at 32 positions.
The instructions for the device were written to a file on the NXT brick using the simplest interpreter – and voilà, it computes! More detailed instructions on how Van den Bos and Landman built the machine are available at www.legoturingmachine.org.
In action, the Lego Turing machine demonstrates how simple a computer actually ease, with every process visible to the casual observer.