Does double the GHz really mean double the speed?

If the gigahertz doubles, does it really run twice as fast?

1. If the gigahertz doubles, does it really run twice as fast?
2. What happens if we swap a 3 gigahertz chip for a 6 gigahertz one?
3. Start at the bank counter.
4. Even the quickest teller runs into one thing.
5. Until the paperwork arrives from the vault there is nothing to do.
6. Twice the hand speed does not shorten the trip to the vault.
7. A CPU is the same.
8. The clock is a beat.
9. On each beat it presses one button.
10. But what if the next value has not arrived yet?
11. Then there is no button to press.
12. That beat simply passes.
13. On the timeline above, a green cell is a beat that pressed a button.
14. An empty cell is a beat that had nothing to press.
15. Push the clock up with the slider.
16. The empty cells do not shrink. They multiply.
17. Now let the numbers turn this around.
18. Fetching one value from memory takes 100 nanoseconds.
19. A nanosecond is a billionth of a second.
20. No person can feel it. To a CPU it is a long time.
21. In that gap a 3 gigahertz CPU lets 300 beats go by.
22. Because there is no button to press.
23. Now raise only the clock, to 6 gigahertz.
24. The 100 nanosecond wait does not move.
25. The clock does not set how fast memory hands the value over.
26. Instead the idle beats go up to 600.
27. What doubled is the idling.
28. What got faster is only the part that was working.
29. When that part is small, the whole barely moves.
30. That is why a server is not chosen by its gigahertz number.
31. When the work is mostly waiting, the clock is not the answer.
32. To sum up.
33. The clock is only the speed of working.
34. It does not shorten the waiting.
35. So how long is that wait, really?
36. The next chapter walks the ladder of waiting.

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