What is "speedstep"

SpeedStep is a series of dynamic frequency scaling technologies (codenamed Geyserville and including SpeedStep, SpeedStep II, and SpeedStep III) built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed (to different P-states) by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat generation.

Enhanced Intel SpeedStep is sometimes abbreviated as EIST. Intel's trademark of "SpeedStep" expired in 2012.