The specific question here relates to overheating laptops, but you may find that the answer also contains some useful general info on automatic-speed switching in mobile CPUs:
Fred, I’ve enjoyed your newsletter for some time now and thought that I might make a contribution based on some recent experiences that I’ve had with my Dell notebook (Inspiron 8200). For awhile now I’ve noticed that my notebook would inexplicably slow down after a relatively brief period of usage. Using the Intel Processor Frequency ID Utility confirmed that my processor speed went from 1.7 GHz to 1.19 GHz. I tried changing a number of settings in both Power Options, and in my BIOS, to no avail. My processor speed was still being reduced to 1.19GDHz. Dell tech support was of no help, telling me that the SpeedStep Technology feature was working as it should at automatically reducing the processor speed.
The problem was that I was operating my notebook on AC power, (it’s also connected to a port replicator) not on battery power, so there was no reason for the processor speed to be reduced.
I came upon the solution to my problem by accident, while examining the rear of my computer while it was turned off and disconnected from its port replicator. I noticed that there were two vents next to each other that housed two separate fans. I blew on one of the fans and saw that the fan blades began to spin. I then blew on the second fan but nothing happened. I then inserted a stylus through the vent and manually moved the fan blades of the non moving fan. The result was that after powering on the computer, now both fans were operating instead of just one. Since then, my processor speed has remained constant without ever being reduced, even when left on all day. Apparently, the heat buildup resulted in a lowering of the processor speed. This fix also solved a number of other problems. I might not even have thought of checking out the fans if I hadn’t read your earlier articles on cooling fans and reducing computer noise. Thanks again for your great newsletter. — Sincerely, Marcel Buchsbaum
(P.S. I guess this is why my wife thinks that I spend too much time on my computer :)
SpeedStep is mainly intended as a power-saving feature to extend battery life on laptops: When it kicks in, it can cut a CPU’s power consumption by 66-75%— a huge amount. But, in the process, the CPU’s speed drops, too. Most SpeedStep-equipped laptops let you play with the settings somewhat to adjust the tradeoffs between speed and power consumption.