In 1944, Grace Hopper was working on the Mark 1 Harvard computer, solving mathematical problems for the US military. The machine had a clock speed of three hertz - three cycles per second. That’s not three million, three thousand, or even three hundred - it’s three. By contrast, today’s processor speeds are measured in gigahertz, billions of cycles per second. In order to get more power out of the machine, Hopper and her colleagues figured out ways to inject more instructions into the machine in what would otherwise have been idle cycles: an early form of parallel processing.

Across the Atlantic, in Bletchley Park, Tommy Flowers faced a similar problem, but adopted a different solution. The Heath Robinson machines intended to break even more complex codes than Enigma, lived up to their name - they were complicated and prone to failure. He proposed to replace the electromechanical relays with vacuum tubes, creating the first ever electronic computer. His colleagues were sceptical, until Flowers and his colleagues proved that a computer could be built from electronic parts, and could run thousands of times faster than the alternative.

In the 1960s, Margaret Hamilton and her team in MIT were writing the software for the Apollo Guidance Computer, the machine that the Moon mission would depend on. The size and weight of the machine were severely constrained, to the extent that the computer architecture only had three binary digits available to encode each command. If you know your binary, you’ll realise that three binary digits only have room for eight numbers - and eight commands are not enough to get a spacecraft to the Moon and back. Hamilton’s team came up with ingenious ways to extend the AGC’s core vocabulary to just under fifty commands - and then built an interpreter to extend the vocabulary even further and code in a language that was easier to understand.