Hi

Although I am not an expert, I thought to have understood as much:

The frequency is given on a per core-basis (often that number is even
referred to as the 'core frequency')


reason

It is all about performance, energy-efficiency and temperature.

In [1, p.3] there is a graph that shows power consumption in dependency
of the performance via over/under-clocking. You can see that a slight
boost of performance increases the power-consumption heavily,
a slight decrease of performance decreases the power-comsumption heavily.

Thus, plot below, two slightly 'under-clocked' cores uses the same power
as one single-core at maximum frequency (not overclocked!) but results in
73% percent more performance.

That's the 'whole' issue. Read more here at intel[2].

Cheers

[1] http://www.intel.com/technology/arch...ad-core-06.pdf
[2] http://www.intel.com/technology/arch...on+tabs_engage