Why is the i7-5960x only 3.0Ghz, while the i7-5930k is 3.5Ghz?

Question

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?

Answer 1

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.