Articles: CPU

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The manufacturer considers Core i7-2600K or Core i7-990X Extreme Edition processors to be specialized overclocker solutions. Both these CPUs have an unlocked clock frequency multiplier that makes overclocking quick and easy. Moreover, Core i7-2600K or Core i7-990X Extreme Edition are manufactured with the latest 32 nm process.  All this means that they may boast significant overclocking potential that can be revealed during overclocking. From our experience with other Sandy Bridge and Gulftown processors we expect our today’s heroes to be able to work stably at up to 4-5 GHz frequencies. This overclocking may deliver substantial performance gain that is why we decided to dedicate the entire chapter of our article to this matter.

When we tested our processors in overclocked modes, we didn’t aim at reaching maximum overclocked frequencies. Instead, we chose a different approach: we tried to identify the frequencies at which our processors could remain stable 24/7 inside air-cooled systems. We had two tests planned for each of our processors. During the first test we determined the maximum frequency, at which the CPU could work stably without increasing its core voltage above the nominal. In the second test we overclocked our processors at moderately raised Vcore (+0.15 V).

During our overclocking experiments, we only changed processor clock frequency multipliers and left the base clock generator frequency (BCLK) at its nominal value for both CPUs. This is the only possible overclocking method for Core i7-2600K, while in case of Core i7-990X Extreme Edition this approach makes things a lot easier in the long run, because it doesn’t require adjusting the multipliers and voltages for the memory, Uncore and QPI bus. We disabled Turbo mode during our overclocking experiments. We used LinX 0.6.4 and Prime95 26.5 utilities to test systems’ stability during overclocking.

As you know, overclocking causes increase in power consumption and heat dissipation, especially, if you increase the voltages in the process. However, we did our best to keep these parameters within reasonable limits. We didn’t disable any power-saving technologies and monitored processor temperatures very carefully throughout the entire session.

Well, our first testing participant, Core i7-990X Extreme Edition, worked stably at 4.26 GHz (+23% above the nominal) without any Vcore increase.

I have to say that this overclocking didn’t have any negative impact on the temperature mode: during our stability tests the processor core temperature didn’t exceed 70°C with our Thermalright Ultra-120 eXtreme cooler.

When we increased the core voltage to 1.4 V, we could get our Core i7-990X Extreme Edition to work at 4.66 GHz, which is 35% higher than the nominal.

However, our stability tests revealed that the operational temperatures grew up substantially. The hottest core was warming up as much as 90°C.

However, this didn’t cause any stability issues whatsoever.

Our second testing participant, Core i7-2600K, works at similar clock speed as Core i7-990X Extreme Edition. So, it showed very similar results during our overclocking experiments. In particular, we managed to speed it up to 4.4 GHz at the nominal core voltage.

In other words, by changing only the processor frequency multiplier we gained 29% higher frequency. As for the core temperatures, they remained very far from critical thresholds throughout all of our stability tests.

Just like Core i7-990X Extreme Edition, Core i7-2600K didn’t warm up to more than 70°C during overclocking without Vcore increase.

As soon as we raised the Vcore by 0.15 V (to 1.425 V), we managed to increase the maximum stable frequency of our test CPU by another 300 MHz (to 4.7 GHz):

In other words, in this case we got 38% past the nominal frequency.

The temperature remained at an acceptable level during the stability tests and never hit 90°C with our Thermalright Ultra-120 eXtreme cooler, which is actually no longer among the most efficient ones.

Although we overclocked processors that are at the top of their lineups, we managed to uncover their significant overclocking potential. This can be explained by the fact that Intel assigned nominal clock frequencies to their processors not based on the maximum capacities of their semiconductor dies, but in accordance with their thermal envelopes. In other words, overclocking may not affect the operational stability, but may lead to serious increase in power consumption and heat dissipation beyond the declared maximums of 95 W and 130 W respectively. However, true enthusiasts do not get scared by problems like that. Contemporary mainboards and cooling systems are robust enough.

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