speed step for mobile processors

[isaacmacdonald]

As you can gather by the table above, the Pentium-M features the same SpeedStep technology that we've seen from previous Intel CPUs. On battery power, the CPU will drop to a noticeably lower clock speed (600MHz in the case of all first generation Pentium-M CPUs).

Was speaking with some other people with p4 laptops and they've said that running benchmarks in linux show no difference between being plugged in and running in battery mode. What's up with that? Is speed step activated soley from bios, or does it run in conjunction with power management???