Turbo Boost and K CPUs

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antiatavist
Posts: 54
Joined: Fri Jan 31, 2014 6:30 am

Turbo Boost and K CPUs

Post by antiatavist » Thu Dec 04, 2014 7:57 am

As I understand it, the ones without the K still have turbo option which enables it to overclock to 3.9GHz, so if you only want to overclock i5 4690K to 4GHZ, it doesn't really make sense to buy the K one?
..
Is this correct?

bastiaan
Posts: 98
Joined: Fri Oct 19, 2012 4:23 am

Re: Turbo Boost and K CPUs

Post by bastiaan » Thu Dec 04, 2014 10:54 am

Some Intel processors have a "Turbo boost" feature allowing them to increase their clock rate to a certain manufacturer set frequency on demand. I think overclocking normally refers to increasing the clock rate to beyond what the manufacturer specifies. Overclocking generally requires an unlocked multiplier, which is what the K in some Intel CPUs refer to.

Still, a case could be made to describe Turbo boost as overclocking by design.

At any rate: I see no point in buying a CPU with an unlocked multiplier if all you want to do is to increase the clock by 0.1GHz over the Turbo boost mode.

washu
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Joined: Thu Nov 19, 2009 10:20 am
Location: Ottawa

Re: Turbo Boost and K CPUs

Post by washu » Thu Dec 04, 2014 12:27 pm

What bastiaan said is mostly correct, except the last part. You cannot overclock a non-K processor even 0.1 GHz over the max turbo speed*. For example, your i5-4690 (non-K) is 3.5 GHz (base) + 0.4 GHz (turbo boost) = 3.9 GHz. It does this by changing the multiplier from 35 to 39. It can't be set to 40 or anything above 39.

Also, turbo does not usually apply to all cores. The i5-4690 can only turbo to 3.9 GHz with 1 or 2 cores active. With 3 cores it drops to 3.8 GHz and with all 4 it drops to 3.7 GHz. For other chips, especially low power and mobile ones, the difference in turbo speed between some and all cores loaded can be significant. The good news is that it is often possible to force all cores to max turbo even on non-K CPUs.

* yes I am aware of BCLK overclocking. It usually doesn't gain much on non-K CPUs and isn't the same thing as changing the turbo multiplier. If you are lucky you might get that 0.1 GHz out of a raised BCLK, but in my experience it's not worth the hassle and potential instabilities VS raising the turbo on a K CPU.

cerbie
Posts: 46
Joined: Sat Dec 28, 2013 3:21 pm

Re: Turbo Boost and K CPUs

Post by cerbie » Thu Dec 04, 2014 2:48 pm

antiatavist wrote:As I understand it, the ones without the K still have turbo option which enables it to overclock to 3.9GHz, so if you only want to overclock i5 4690K to 4GHZ, it doesn't really make sense to buy the K one?
..
Is this correct?
No. It is running within spec, and so is not overclocking. If you want to run it at 4GHz, you would need to be able to set that. Turbo Boost let's the CPU decides on its own what speed it should be running at, within specifications, at a given p-state (that 3.9GHz is as fast as it will stay, with one active core, and faster than it will run with more cores active, not considering very short bursts).

With the exception of the i7-4790K (faster base speeds than the i7-4790), the K CPUs allow overclocking, while the non-K do not, and are otherwise the same. Your chances of overclocking a non-K CPU on LGA1150 by even as much as 5%, are very small, since the base clock is relied on by much of the CPU and chipset. If you want to make sure you can run all cores at 4GHz, FI, you would need to overclock, or buy an i7-4790K.

antiatavist
Posts: 54
Joined: Fri Jan 31, 2014 6:30 am

Re: Turbo Boost and K CPUs

Post by antiatavist » Fri Dec 05, 2014 1:43 am

So, you're saying there would be a considerable performance difference, even if i5 4690k were to be overclocked only to 4GHz, compared to non k?

washu
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Location: Ottawa

Re: Turbo Boost and K CPUs

Post by washu » Fri Dec 05, 2014 7:47 am

antiatavist wrote:So, you're saying there would be a considerable performance difference, even if i5 4690k were to be overclocked only to 4GHz, compared to non k?
I don't think anyone is saying that. It's such a small difference it would be hard to notice.

Here how i5-4690 non-k runs (assuming proper cooling):
1 or 2 cores active: 3.9 GHz
3 cores active: 3.8 GHz
4 cores active: 3.7 GHz
4 cores active and "overclocked" on a Z97: 3.9 GHz

Even without the Z97 forcing all cores to max it would be really hard to notice the difference between an i5-4690 and a i5-4690K @ 4.0 GHz. Only if you run the K faster would the difference become worth it.

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