  ‘Effective’ means doing, not merely imagining or postulating. At this stage neither Turing nor any other logician made a serious investigation into the physics of such ‘doing.’ But Turing's image of a teleprinter-like machine does inescapably refer to something that could actually be physically ‘done.’ His concept is a distillation of the idea that one can only ‘do’ one simple action, or finite number of simple actions, at a time. How ‘physical’ a concept is it?