The embedded power control unit added also power sensors for each core. So the CPU knows how much power each core is consuming and how much heat is being dissipated. This allowed the addition of a “Turbo Mode” in the CPU.

Turbo Mode allows the CPU to increase the clock rate of the active core(s). This idea isn’t new and Core i7 isn’t the first CPU to use it (some Xeon CPUs based on Netburst – i.e. Pentium 4 – architecture have this feature, known as “Foxton technology”). But on the previous incarnation of this technology it could only be used when the other processing cores were idle.

This new mode is a closed-loop system. The CPU is constantly monitoring its temperature and power consumption. The CPU will overclock the active cores until the CPU reaches its maximum allowed TDP, based on the cooling system you are using. This is configurable on the motherboard setup. For example, if you say your CPU cooler is able to dissipate 130 W, the CPU will increase (or reduce) its clock so the power currently dissipated by the CPU matches the amount of power the CPU cooler can dissipate. So if you, for example, replace the CPU stock cooler with a better cooler, you will have to enter the motherboard setup to configure the new cooler TDP (i.e. the maximum amount of thermal power it can dissipate) in order to make Turbo Mode to increase the CPU clock even more.

Notice that the CPU doesn’t have to necessary shut down unused cores to enable Turbo Mode. But since this dynamic overclocking technique is based on how much power you can still dissipate using your current CPU cooler, shutting down unused cores will reduce the CPU consumption and power dissipation and thus will allow a higher overclocking.

The new Turbo Mode is an extension to the SpeedStep technology, so it is viewed by the system as a SpeedStep feature.

It only works for the CPU cores, so the memory controller and the memory cache are not affected by this technology.

Apparently Turbo Mode will only be available on “Extreme Edition” models.