Power gating and turbo mode: Intel talks Nehalem at IDF

Most of the Nehalem disclosures in Gelsinger's keynote, and in the subsequent technical session on Nehalem, had to do with the new microarchitecture's power management capabilities. With Nehalem, Intel is introducing a technology that it calls "power gating." Traditionally, Intel has been able shut down an unused core by cutting its active power, but even though it's in a sleep state, that core is still dissipating plenty of power because of leakage current. Intel's power gating technique involves a new transistor design, and it lets Intel cut the leakage current, as well, so that the sleeping core's power dissipation drops to near zero.

When one or more of the cores on a Nehalem chip are powered down, the processor can divert extra power to the cores that are in use by increasing their clockspeed and voltage. (This is kind of like the "divert power to the main thrusters," thing that Scottie would always do in Star Trek.) This gives the active cores extra performance headroom while permitting the overall processor to remain in the same power envelope, and Gelsinger noted that it effectively gives each core two extra speed bins worth of performance.