I recently installed Ubuntu Linux 8.10 on a Compaq Presario 2100 laptop. Specifically, this model of the 2100 series has an intel Celeron mobile processor which nominally runs a 1.7Ghz.
Naturally, on a laptop you don’t want to be running you CPU at full-chat all the time as the fan can be noisy and the flesh on your legs may burn. By default, Ubuntu didn’t work out how to step down the speed of the CPU which is unusual.
I could swear that I’d had this laptop throttling it’s cpu frequency before and with a little brain wracking and internet searching, I [re]found the solution.
You need to activate the p4-clockmod module using the command sudo modprobe p4-clockmod. Once this is done, you can activate the Gnome panel cpu frequency applet (right-click panel>Add to panel>CPU Frequency Scaling Monitor)
You should now be able to choose a speed from 1.7Ghz down to 212Mhz from the list or select one of the automatic speed governors.
You still need to make sure that the kernel module is loaded every time at boot time. To do this, use sudo gedit /etc/modules and add the line p4-clockmod.
Now, every time your machine starts, the cpu governors will be activated and you’ll hopefully have a quieter and cooler experience.