Intel Sandy Bridge Core i5-2500K & Core i7-2600K Processors Review

Author: MAC
Date: January 2, 2011
Product Name: Intel Core i5-2500K & Core i7-2600K
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Overclocking Results

As most of you know, there's been an immense controversy regarding how Intel was handling/enabling overclocking on Sandy Bridge processors. Regrettably, most the negative rumours are true. However, they perhaps don't matter. Read on.

Because of the unprecedented level of integration on Sandy Bridge (ie: just about everything is now on CPU itself), including the clock generator that used to be on the motherboard, there is very little headroom when it comes to the BCLK. Right now it appears that 104-106Mhz is likely the average, with a few chips being able to hit 109Mhz, if not slightly above. It just depends on the quality of the silicon. As a result, the bulk of the overclocking will have to be done via the CPU multiplier. Regular locked, or 'limited unlocked' as Intel is calling them, Sandy Bridge chips come with up to 4 additional performance bins, but only when combined with a P67 motherboard (there's really no CPU overclocking at all on H67). These are bins that are above the usual Turbo Boost bins, so there is a fair bit of extra performance to extract even if you don't buy an unlocked K-series chip.

However, even if you buy a K-series chips, your success is not guaranteed. Each chip is unique, and each will have a different highest stable CPU multiplier. Some chips will have a functional 53X multiplier, some will not be able to go above 44X, for example. This is now obviously the #1 factor in whether your chip will be able to overclock well or not. Max Multiplier + Max BCLK = Max Clock Speed, totally idiot proof. Only a lack of voltage or cooling can prevent you from reaching that Max Clock Speed once you've determined the multiplier and BCLK limits. No tweaking or fancy skills necessary, at all. Also, an overkill of voltage or cooling will not really help you gain additional headroom once the max has been found.

Based on a third-party's extensive testing of 100 retail D2 stepping processors, this is how Sandy Bridge is shaping up on the overclocking front:
  • Approximately 50% of CPUs can go up to 4.4~4.5 GHz
  • Approximately 40% of CPUs can go up to 4.6~4.7 GHz
  • Approximately 10% of CPUs can go up to 4.8~5 GHz (50+ multipliers are about 2% of this group)

As you can see, at this point in time, unlocked K-series Sandy Bridge chips overclock quite well. Not amazingly well, but quite well. They perhaps won't match many people's expectations, but few things are able to satisfy the hype in the computer realm. Having said that, we know of at least one or two tweaks being worked on right now that have shown some promise in helping raise the max multiplier on chips with an abnormally low max multiplier. Nevertheless, hardcore overclockers will obviously have a certain disdain for this iteration of Sandy Bridge, as they should, and they would be well advised to wait for the LGA2011 Sandy Bridge platform, which has been rumored to be more overclocking friendly both with respect to BCLK headroom and sub-zero scaling.

On a side note, we highly recommend that users not use a vCore above 1.375V-1.40V for 24/7 use. Because of the fact that Sandy Bridge processors run so cool it will be exceedingly tempting for overclockers to want to run with 1.50V in order to stabilize a 5Ghz+ core frequency, but we recommend against this. We have all been spoiled by the bulletproof nature of Intel's recent chips, but this a brand new class of processor, and we absolutely expect there to be a steep learning curve for the first 6-8 weeks with regard to how far these chips can be pushed. If you don't want to be one of the unlucky ones who will inevitably kill their new 2500K/2600K soon after launch, heed our warning and play it safe with the vCore.

So what were we able to achieve? Well given how little time we had on our hands, we decided to find out what the max multiplier and highest BCLK were for our two chips, instead of doing our usual stability tests.

Highest CPU Multiplier

Highest BCLK

Not too bad. Given our max multipliers and max BCLK's, we can potentially clock our i7-2600K up to 5029Mhz and our i5-2500K up to 4935Mhz. We definitely look forward to testing out stability at these speeds in our upcoming P67 motherboard reviews.

Despite all the Doom & Gloom from ourselves and hardcore enthusiasts everywhere, 99% of people who overclock will ultimately not care about the BCLK limitations, since it just makes the overclocking process easier. There is very little that you need to tweak with Sandy Bridge in order to achieve a very nice overclock. All you need is a K-series processors and a P67 motherboard, and you will be hitting 4.4Ghz and above in a matter of minutes. Having said that, the fact that you have to pay ~$30 more for a chip that overclocks properly totally betrays the value-minded principle that was originally behind overclocking, but that's a debate for another day.

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