How Does It Work?

Unlike manual overclocking, the Intel Turbo Boost Technology does not keep the processor cores overclocked all the time. Instead, it only kicks into action when the operating system requests the highest ACPI performance state, P0. This occurs whenever a CPU-intensive software is actively using the processor.

Depending on the processor model and several other variables, the processor will dynamically overclock one or more of its processing cores to boost its performance. The amount of overclocking performed is determined by an algorithm that takes into account these factors :

• Processor Model - different processors have different limits on the amount of overclocking allowed
• Number Of Active Cores - the amount of overclocking for each active core depends on the number of active cores.
• Power Delivery Limit - the amount of power the processor can draw from the motherboard
• Estimated Processor Current Draw
• Estimated Processor Power Consumption
• Processor Temperature

When the Intel Turbo Boost Technology is engaged, the processor will continuously monitor its current draw, power consumption and temperature. If they are all below Intel's pre-set limits, then the processor will automatically increase the clock speed of the active cores in steps (speed bins) of 133 MHz up till the upper limit allowed by the processor model.

Conversely, if the current draw, power consumption or temperature exceeds the Intel's pre-set limits, then the processor will automatically reduce the clock speed of the active cores by one speed bin (133 MHz). It will then re-evaluate the variables to decide if a further clock speed reduction is required. The clock speed boost will also be reduced if the processor becomes idle.

The processor will continuously monitor the operating system's requirements, and the variables above to dynamically overclock the processor cores as required. Unless specifically programmed to detect these changes, most software will not be aware of the overclocking performed by Turbo Boost. However, this is only a problem for users who need to know the processor's exact clock speed (e.g. reviewers).

Switching It On

The Intel Turbo Boost Technology is enabled by default in all Intel Nehalem-based processors, e.g. Intel Core i7 and Core i5 processors. Unless you know what you are doing, you should leave Turbo Boost enabled for the extra boost in performance. However, there are some circumstances when it is necessary to turn off Turbo Boost.

Most notably, reviewers testing the Intel Nehalem-based processors should turn it off for MHz-to-MHz comparisons against other processors. Otherwise, the test results would be skewed in favour of the Intel Nehalem processors. This is the reason why we advise users of our x264 HD Benchmark 3.0 to turn off Turbo Boost if they are using a Nehalem-based processor. Please see this article for the full details.

Overclockers should also turn off Turbo Boost as it may affect the stability of their overclocked processors. When you have a Core i7 processor running at over 4 GHz, even a small 133 MHz overclock by Turbo Boost can cause the processor to crash. Turbo Boost's dynamic assessment of the processor's current draw, power consumption and temperature may provide some protection against that, but it cannot guarantee the system's stability. Therefore, overclockers are advised to disable Turbo Boost.

To this end, most motherboards have a BIOS switch that allows you to turn off Intel Turbo Boost Technology (see Intel Turbo Mode Tech). Some even include an option for you to increase the number of speed bins allowed but this is only applicable for the Extreme Edition processors which have unlocked multipliers.

Support Tech ARP!

Help support our work by visiting our sponsors, participate in the Tech ARP Forums, or even donate to our fund. Any help you can render is greatly appreciated!