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For example, if we're considering an quad-core processor, and if the speed given in the "specifications" is 1.8 GHz, does that meant that the combined speed of the entire set of 4 cores is 1.8 GHz, or that each of these four cores has a speed of 1.8GHz individually?

In other words, if the printed spec is "quad-core 1.8 GHz", does that mean that there are 4 cores of speed 1.8 GHz?

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Frequency is not cumulative. The chip runs at 1.8 GHz, each of the cores runs at 1.8 GHz, all four cores run at 1.8 GHz. If one car travels at 100 km/h and another car runs beside it at 100 km/h, you just have two cars running at 100 km/h, you don't have anything running at 200 km/h.

Instruction execution rate, on the other hand, is cumulative. If a single-core processor running f GHz can execute k instructions per second, then an n-core processor running at f GHz can execute nk instructions per second*, just as our two cars together carry twice as many people as one car.

*In practice you won't see an n-fold increase in speed, as some resources are consumed in co-ordinating the cores.

  • Okay. So, for practical purposes. Would you choose a 1.3 GHz hecta core processor (Yes, I understand that in the real world, hecta = 4 + 4, and not 8 individual cores) or say, a 1.9 GHz quad-core processor, everything else being the same (brand, model etc.) Thank you – WorldGov Jul 27 '16 at 9:40
  • I suspect you meant octo-core. (Octo = 8; hecto = 100. A hecto-core system would be considered many-core, which is an entirely different beast.) In any case, the answer depends on what you want to do. A single, single-thread app would run faster on the 1.9 quad, as would a small number of single-thread apps. If you have many background processes, on the other hand, or an app that does a lot of preforking like Apache, you'll likely find the slower chip gives better performance overall, since each process gets roughly twice as many chances to be in core. Better still is a multi-threaded app on – Darwin von Corax Jul 27 '16 at 18:51
  • an OS that supports thread-level parallelism (as, AFAIK, Android does) in which case individual apps may perform significantly better. All this is a long-winded way of saying that in a phone I would likely go for more cores over more Hz. – Darwin von Corax Jul 27 '16 at 18:52

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