O Pentium 4 630 vem com SpeedStep que diminui quando a carga é menor para reduzir o consumo de energia / aquecimento.
SpeedStep is a trademark for a series of dynamic frequency scaling technologies, 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 dissipation. Enhanced Intel SpeedStep is sometimes abbreviated as EIST.
Esta é a causa das variações