the chip is designed to change speed, it runs at a lower speed whenyour doing stuff like word processing or browsing. But as soon as it see's you need more power it ramps up the frequency and also the voltage. try playing arealy big movie file or playing a game or running a benchmark, you will see it goes to it's full speed then. You should not need it on full power all of the time.
That is Intel's Speedstep. Reduces CPU voltage and clock when CPU usage is low to save power. Gives you only the performance you need as you need it. Doesn't help idle a ton though as Intel already gave the chip the capability to turn sections off, helps more in the intermediate ranges.
(And yes, it is in the BIOS and should be able to be deactivated if you wish (no idea why you would want to unless OCing) under advanced core options (or the like)).