Clarification request: Have you looked in your BIOS ...
for settings for speed step?
Advanced BIOS Features, CPU EIST Function and C1E functions
C1E enhanced halt state — Introduced in the Pentium 4 500J-series processors, the C1E halt state replaces the old C1 halt state used on the Pentium 4 and most other x86 CPUs. The C1 halt state is invoked when the operating system's idle process issues a HLT command. (Windows does this constantly when not under a full load.) Entering halt state, which is a lower-power state, will cut a CPU's power consumption and heat production. Intel's new C1E halt state is also invoked by the HLT command, but it turns down the entire CPU's clock frequency (via multiplier control) and voltage in order to work its mojo. This more robust halt state requires significantly less power than the old C1 implementation.
C1E halt cranks the CPU bus multiplier down to its lowest possible level on the 600-series processors, which is 14X, so a P4 660 processor with the C1E halt state active actually runs at 2.8GHz. I believe that C1E halt is also a binary condition invoked by the HLT command; it's either on or it's off.
Enhanced SpeedStep — SpeedStep also modulates the CPU clock speed and voltage according to load, but it is invoked via another mechanism. The operating system must be aware of SpeedStep, as must the system BIOS, and then the OS can request frequency changes via ACPI. SpeedStep is more granular than C1E halt, because it offers multiple rungs up and down the ladder between the maximum and minimum CPU multiplier and voltage levels.
Intel cites its mobile products when talking about SpeedStep, which is apt but not entirely helpful because it conjures up images of the Pentium M processor, a very different beast. The Pentium 4 doesn't contain most of the heroic power-saving measures of the Pentium M.
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