I have an old laptop I'd like to repurpose as a print/SSH server (among a few other light tasks). The laptop has a 2.0GHz Pentium M processor with 1GB of RAM (to be specific, its an old Dell Precision M60). The system is running Ubuntu Server 10.04. A combination of htop and my screen config show that the CPU is constantly running at its full speed, even when under little/no load -- this was not an issue under 9.04 and 9.10. I'd like to drop the speed of the processor down to save on power, heat, and noise.
Is there any way that I can force the system to only run at 600MHz.
You could under clock the processor at the hardware level through BIOS. Here's a guide for overclocking that specific model (you'll want to do just the opposite ;):
http://www.overclockers.com/forums/showthread.php?t=277264
I wouldn't trust software that claims to do this but that's just a personal BIOS (lame pun). I've seen it done for video cards.
You don't need to use the BIOS. There's some stuff in /sys/devices that'll set the CPU Scaling factor
Have a look at this guide: http://embraceubuntu.com/2005/11/04/enabling-cpu-frequency-scaling/ It can explain more than I can easily