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Intel Core i7 and Core i5 LGA 1155 Sandy Bridge
by Damien Triolet, Franck Delattre, Guillaume Louel et Marc Prieur
Published on March 21, 2011

Overclocking in practice
To start with, we wanted to test overclocking by the DMICLK, on an Intel DP67BG motherboard and a Core i7-2600K, which is at a base of 100 MHz. As expected, there’s not much room for manoeuvre and we weren’t able to stabilise performance at anything higher than 106 MHz. We’re pretty much limited according to Intel’s wishes in terms of the multipliers here then.


On the Intel DP67BG card at least, the base multiplier can’t be increased and you have to overclock by increasing the turbo mode multipliers. To move up to 4 GHz, you simply set them all at 40, for 1, 2, 3 and 4 active cores that is. There’s a nuance here in comparison with standard overclocking because if the CPU exceeds its TDP, it will return to its base multiplier after one second because of Turbo 2. You can set this delay at 32 seconds, but it’s actually better to raise the turbo mode power threshold to, say, 120 watts from 95.

We started with the Core i7-2600K, that we were able to stabilise at 4.1 GHz in Prime95 at its base voltage of 1.2v, compared to 3.4 GHz by default and 3.5 GHz in Turbo for 4-core. At 1.3v we got up to 4.4 GHz, then 4.7 GHz at 1.4v. At this setting, the CPU energy consumption is at 155w, against 74w in its base configuration.

L'overclocking du 2600K

We managed to stabilise the 2500K at 4 GHz at 1.2v, 4.3 GHz at 1.3v and 4.6 GHz at 1.4v, enabling the Internal PLL Voltage Override function after 4.4 GHz. At 4.6 GHz and 1.4v, the CPU consumes 130w in load, against 61w by default.

L'overclocking du 2500K

Like all the non-K CPUs, the Core i5-2400 is only partially let off the leash in terms of its multiplier (limited to +4). By default the multiplier is fixed at 31, but can go up to 32, 33, 33 and 34 in turbo with 4, 3, 2 or 1 active cores. With four active cores, you can therefore clock it at 3.6 GHz at its default voltage of 1.2v, and even 3.81 GHz by increasing the DMICLK to 106 MHz. Energy consumption is, then, 75w, compared to 60w by default.

The Core i5-2300, with a base clock of 2.8 GHz, can reach 3.3 GHz with 4 cores active simply by adjusting the multiplier, and 3.49 GHz by adjusting the bus too. We kept its voltage at 1.2v and energy consumption was then 69 watts, compared to 54.5w by default.

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