0

Why is the i7-5960x only 3.0Ghz, while the i7-5930k is 3.5Ghz? I was really looking forward to the 8-core intel i7, until I saw the stock clock speed was lower than it's 6-core counter part. Is there any particular reason this is? I would have expected them to at least have the same core clock.

Doing some quick math:

  • 6 cores @ 3.5Ghz = 21.0Ghz total from all cores (spread across 12 threads)
  • 8 cores @ 3.0Ghz = 24.0Ghz total from all cores (spread across 16 threads)

Am I looking at this correctly? What exactly does it mean in terms of performance? Is the i7-5930k simply better/faster PER CORE/THREAD?

5
  • 2
    Briefly, it's harder to get 8 cores to run at a specific speed than it is to get 6 cores to. Oct 27, 2014 at 12:44
  • 1
    Related: CPU Cores: The more the better? Oct 27, 2014 at 12:46
  • 1
    Come on, if you put a second engine in a car, it won't run twice as fast, now wouldn't it? Oct 27, 2014 at 12:50
  • Your "quick math" is incorrect. You don't add the frequency of each core in a multi-core processor. The actual performance difference that you will see between 3.0Ghz and 3.5Ghz is not really significant compared to capability of running 2 additional threads. Besides the 0.5 Ghz boost frequency makes the i7 5960 actually better compared to the 0.2 Ghz boost frequency of the i7 5930
    – Ramhound
    Oct 27, 2014 at 13:08
  • Ramhound, I know you don't really add up the clock speed (core frequency) from each core the way I did, but I was looking for a way to represent the total number of cores on each CPU @ their respective stock frequency in order to try and simplify things for myself.
    – DaedalEVE
    Oct 28, 2014 at 1:17

1 Answer 1

3

Why? To be sure ask Intel. They decided on this. A likely reason tough is power and heat.

  • More cores means more power needed and more heat generated.
  • Higher clock speed means more power needed and more heat generated.

It might well be that 8 cores at 3.GHz exceeded the power budget, at which time you only have a few choices:

  1. More expensive cooling, beefier power supply, etc etc.
  2. Use a lower max clock rate.
  3. Use less cores.
  4. Pick the best chips. (This works marginally. If 1 out 10 chips works better and gerates less heat then throwing away the other 9 gets expenive.)

A good guess is that Intel looked at their chip capabilities and selected the chips most suiting to the market requests. That means both chips with many cores and chips with high clock speed. And often not both at the same time.

As to the 'quick math': Your sum of GHz does not match actual computing speed.

Two cores at 1GHz (just a round number) might be twice as fast as a single core at 1GHz. Or they may be 10 times as fast since with two cores you can get twice the cache (assuming that all data fits into twice the cache but not into 1x cache size). It may also be slower. (e.g. a task hopping from one core to the other, leading to cache misses).

In short: Cores x GHZ != CPU speed.

5
  • Intel's implementation of both virtual cores (i.e. Hyperthreading) and physical cores is interesting. In the case of Hyperthreading each physical core simply as the capability of processing two threads at once. So the clock frequency of a multi-core ( both virtual and physical ) cannot be added together since each physical core is actually independent from one another.
    – Ramhound
    Oct 27, 2014 at 13:20
  • True. I ignored that since both mentioned processors have 6 resp 8 real cores. No need to add more (and more complex) information.
    – Hennes
    Oct 27, 2014 at 13:33
  • I suppose my comment was more about your comment about his "quick math" more than anything. Because both products do have Hyperthreading.
    – Ramhound
    Oct 27, 2014 at 13:43
  • Ah! So on the i7 5960 all 8 cores add up to 3.0Ghz total? That would mean each core on it's own is only 375Mhz?
    – DaedalEVE
    Oct 28, 2014 at 1:39
  • No, 8 cores at 3.-GHz for the i7 5960 means that the base speed for all 8 cores is 3.0GHz. It ignores the ability to briefly turbo up to 3.5GHz which can be done when a single core is running, the other 7 cores are idle ans the chip is not hot. It will throttle back when that turbo'd core or the chip gets hot. There actually is much more to this. Enough to fill pages with.
    – Hennes
    Oct 28, 2014 at 5:44

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .