What regulates Intel SpeedStep CPU throttling? Can I get some control of this on Windows7?

Since none of the answers take on what speed step does exactly and how to disable/enable it here is what I found:

Let's look at how it works. SpeedStep has two key components:

C1E (Enhanced Halt State): C1E is the simpler of the two components. It can be enabled or disabled in the BIOS, and performs independently of the operating system. C1E has two configurations - idle, and load. When CPU usage is relatively low, this feature lowers your processor's multiplier to its lowest setting (usually 6x) and slightly lowers its vCore. During a CPU-intensive application, it will raise the multipler to its maximum value, and will provide a small boost in vCore to compensate. In our example, C1E will make your processor run at either 6x or 9x the FSB.

EIST (Enhanced Intel SpeedStep Technology): This is a very robust feature and has a wide variety of power-saving capabilities. Like its simpler cousin, EIST can affect both your CPU's voltage and it's multiplier - however, it has many more levels of configuration. Instead of a simple "slow or fast" setting, SpeedStep can utilize all of the available multipliers. In our example case, EIST will allow your processor to run with a multiplier of 6, 7, 8, or 9, and chooses which one to use based on how much demand your CPU is under. EIST is controlled by Windows, and utilizes the different "power schemes" you may have seen in your control panel.

It sounds like SpeedStep can be found in either the BIOS or the OS and maybe even both. My guess is that DELL maybe lying to you about the performance, I say try disabling it and see what happens.

To disable it under windows, select the Power Options and select High Performance. Make sure that the minimum and maximum processor states are 100% and the System Cooling Policy to be Active.

Here are two supporting forums and a site that may help you out:

SpeedStep Guide

Let's Talk about C1E

Bay Wolf's Speedstep FAQ

Update: adding an active laptop cooler has completely resolved this issue. When the overall temperature is kept down this throttling does not kick-in at all, and I can sustain a full processor load indefinitely.

Thanks for the good info in the other answers. I think I've been able to put together an idea of what is going on:

There are elements of speedstep that can be controled by the BIOS, and also by the OS. In windows 7, the power scheme preferences (minimum processor state, active/passive cooling, AC/DC power) are primarily what guides the OS in setting the processor speed.

Some simple experimentation on this laptop, indicates that something is down-regulating the CPU in response to temperature. It could be the BIOS, or the Dell chipset/drivers.

If I let it idle until the fan spins down and the air venting out the side is room temperature, and then I start a 7-zip benchmark, I get about a minute and a half of full-speed CPU. About the time the exhaust air is too hot to keep my finger there, the CPU starts throttling down until it eventually gets as low as 667 MHz. Then it gradually steps back up to nearly full-speed for about 40-60 seconds, and then the cycle of throttle-back and cool-down begins again. The whole cycle takes about three minutes.

Given the obvious heat-sink and fan size/weight/power constraints in a laptop, I can understand that the system needs a backup method to prevent overheating. I also understand why I can't or shouldn't override this, even if I could figure out how to do so. Basically I can only expect to get full speed from my processor for brief bursts of time until the total heat build-up is too much, then it has to throttle back while that heat is dissipated.

I guess putting 2.8 GHz in a laptop gives you some good bursts of speed when you need it, but it simply can't have the same stamina as a workstation.

Check the 'System cooling policy', the next item in the power window. It should be set to active (when plugged in), so that increases in processor temperature increase the fan speed, rather than decreasing the processor freqency (passive).