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How far do electrons physically move in a single clock cycle in a (theoretical) 4GHz processor?

How far do electrons physically move in a single clock cycle in a (theoretical) 4GHz processor?

I was musing last night about computers and processors and this video of a 6-bit digital adding machine, and I know that 4 GHz seems to be the practical limit of mass-produced CPUs of the current era. Why is that the case? I was trying to imagine something like that 6-bit adding machine * 11 (ok, 10.6666...), lined up side by side, and operating 4 billion times in a second. It's mind-bending to me. XKCD has another take on it.

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Total answers/comments: 1
bert [Entry]

"Each electron hardly moves at all in 0.25 ns, even with the tens of amps that flow in such processors.

""For example, in a copper wire of cross-section 0.5 mm2, carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second.""Wikipedia

Fortunately, we don't need the electrons to move very far to carry a wave that moves long distances very fast."