The Clock: One Action at a Time
We have cells that store numbers and a processor with a handful of actions. The third and last assumption of the idealized machine answers a question you may not have thought to ask: how does time work inside the machine? The answer is stricter than anything in ordinary life — and two of the most dramatic moments of the whole course are hidden inside it.
Start with the question
Watch your screen: music plays while a page scrolls while a download ticks forward. Obviously the machine does many things at once — obviously time inside it flows like ours, full of parallel streams. Right?
Wrong — and the truth is stranger. Our idealized machine lives by a metronome. Tick: exactly one action from the processor's small set. Tick: exactly one more. Never two at once, never a pause where "something happens on its own", never an action between ticks. Machine time is not a river; it is a staircase climbed one step at a time.
The clock rule and its two faces
The rule: the machine performs exactly one action per tick; actions follow one another in strict sequence.
Two consequences are folded into that one sentence, and they deserve separate shelves in your head: