The details were a bit hazy. This was not a blueprint for an actual machine, rather a thought experiment that Turing had dreamed up in order to resolve an abstract riddle from the completely impractical world of pure logic. Waterhouse knows this perfectly well. But he cannot get one thing out of his mind as he sits there atop the blast walls at the dark intersection in Bletchley Park: the Turing machine, if one really existed, would rely upon having a tape. The tape would pass through the machine. It would carry the information that the machine needed to do its work.