Voices of Science

The computer was built on these Post Office racks, which were six foot six tall and just about two feet wide, with holes up the sides of the uprights. The equipment was made on a chassis, two foot wide, which could be screwed to these fixing holes. So when I first arrived in Manchester there were probably a couple such racks with half a dozen or ten chassis units fixed to them. And we built up the computer by drawing out circuit diagrams of further units. Tom and I would design an eight valve circuit. Tom would do it in the train on his way to and from Dewsbury, where he was living, I would do it at home. We had – it was Norman, you’d give him a circuit diagram and he could then wire up the – the chassis in accordance with the circuit diagram. And I think he got promoted in the university’s hierarchy and he was replaced by a young woman, Ida Fitzgerald, I remember her name, who was extremely efficient. She understood what was required from the circuit diagram and she executed the thing correctly, and she did very quickly too. We would screw it into a Post Office rack and connect it up to all the other units, and then start to find out why it wasn’t working properly. And we thought it was very important to have something that worked, did something or other, at every stage as we built up these units. The very last thing we could contemplate doing was to design the whole thing and have it all built and wire it all up, and then find out why it didn’t work. It was essential that the whole thing would work together at every stage, as you added one unit after the other. It was necessary that the apparatus should do something, which we could see was correct, and if it wasn’t correct we could mend it until it was correct, at every stage, every chassis that we connected up. Well we went on with this process of adding the units and making the whole lot do something together at every stage, until we got to the stage when we’d made a computer. [Laughs] Tom and I commissioned this last unit and we laboriously fed in a few binary numbers and switched it on, and we saw the thing had done a computation.