"The key feature!" Waterhouse says brightly. "See, these ETC card machines are great for input and output. We’ve got that covered. The logic elements are straightforward enough. What was needed was a way to give the machine memory, so that it could, to use Turing’s terminology, bury data quickly, and just as quickly disinter it. So I made one of those. It is an electrical device, but its underlying principles would be familiar to any organ maker."