Intel SpeedStep Technology
SpeedStep is a processor feature that requires BIOS and OS-level support. When enabled, the operating system will trigger a processor clock speed reduction by adjusting the clock multiplier. Pentium 4 or Pentium D processors adjust the multiplier to x14, which, in case of FSB800 speed (200 MHz base clock), results in a 2.8 GHz processor clock speed. Since Core 2 duo runs at different voltages, a higher system bus speed and lower core clock speeds, the multiplier change had to be adjusted as well.
Core 2 Duo processors with SpeedStep enabled will switch to the x6 multiplier, which results in an effective processor clock speed of 1.6 GHz at 266 MHz system bus speed (FSB1066). At the same time, the core voltage is set to only 0.9 V. Doubling the clock speed triggers a four-fold increase in power consumption, so reducing both the clock speed and the operating voltage helps to dramatically reduce power consumption and heat dissipation.
SpeedStep comes into action when the processor load falls under a certain threshold. In order to adjust processor performance and power requirements to ideal levels at varying loads, Core 2 Duo processors can run at all multipliers in between x6 and their maximum multiplier.
Core 2 Duo runs at only 0.9 V core voltage and 1.6 GHz core speed when SpeedStep is in action.
Ultra Fine Grained Power Control
Core 2 processors are able to shutdown all the parts of a processors that do not need to be active. This does not only come into effect when the processor is running at low loads or even idle, but it is equally important in high-load scenarios: Certain logical units might be unused although the processor is doing some heavy-duty work.
In this example, the green elements represent processor logic that is not required to perform a given task. These units can be shutdown to save energy.