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Turbo Mode

You may think that the theoretical info we shared above is more than enough to move on to Core i7 practical overclocking experiments. It is partially true. However, the harmonious structure of interconnected multipliers, voltages and frequencies gets slightly messed up by additional innovations introduced in the new generation processors. I am talking about Turbo Boost Technology – sort of dynamic overclocking integrated by Intel into their new CPUs.

I would like to remind you that Turbo Boost implies the ability of the processor to increase its frequency multiplier over the nominal value if it doesn’t push the power consumption over the set threshold of 130W. The current implementation of this technology allows Core i7 processors to have their multiplier increase by 2 if there is only one core loaded with work, and by 1 if most cores are utilized.

The CPU seems to be treating its own multiplier pretty frivolously, so you may think that it could hinder overclocking. However, it is not quite so in reality. On the contrary, those overclockers who decided to go for an LGA1366 system, get an additional tool that may come in handy.

The simplest way is to disable Turbo Boost in the mainboard BIOS. All mainboards for Core i7 processors have this option. Moreover, Turbo Boost technology is directly connected to another technology working with the CPU clock frequency multiplier – Enhanced Intel SpeedStep. As a result, turbo-modes can only be activated when EIST is on. Many overclockers are used to disabling power-saving technologies, which means they automatically lose Turbo Boost.

However, you may not ignore this turbo-mode but use it to your own advantage. The thing is that the BIOS of most LGA1366 platforms allow disabling the processor’s ability to control its power-related parameters without deactivating Turbo Boost. This trick makes it possible to statically increase the processor clock multiplier by 1 over the nominal independent of the workload and its current level of power consumption. As a result, Core i7-920 processor with the default multiplier at 20x can work with 21x multiplier, and Core i7-940 – with 23x multiplier, which its nominal setting is only 22x. Of course, this raise doesn’t look serious enough, but together with increased BCLK frequency it may actually help to achieve better overclocking results.

Here I would only like to add that we do not recommend using turbo mode directly according to its intended purpose, which is also quite possible. Although dynamic increase of the frequency multiplier that occurs during lowering of the workload may do no harm in nominal operational mode, it may cause serious instability during overclocking. The problem is that when you change the BCLK frequency to overclock your processor, the frequency increases more if the multiplier increases. As a result, the CPU may over-overclock itself past the stability threshold when Turbo Boost kicks in. So, you may end up with a processor that successfully passes all stability tests, but when it tries to switch to turbo mode under reasonable workload, the system loses stability.

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