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Turbo Boost

From dankwiki

Intel introduced Turbo Boost (previously known as "Intel Dynamic Acceleration") in the Nehalem processor. It allows active cores to be stepped up beyond their usual operating frequency, using cutoffs such as power draw or thermal dissipation. Turbo Boost operates in 133MHz increments on Nehalem, and 100MHz increments on Sandy Bridge; the Sandy Bridge implementation also uses a more accurate thermal model. Turbo Boost can be used on more than one core at a time; Sandy Bridge typically allows more aggressive Turbo Boosting when multiple cores are active.

"Activity" is a function of the ACPI Processor State ("C State") of each core; cores in state C0 (Operating) or C1 (Halt) are considered active.