The biggest reason you would want to scale the frequency of your CPU is that you want to conserve electricity. Now on a desktop, you might not it's not so important, unless you are really conservative with your electricity bill.. but you might want to have your desktop scale it's frequency down really low to conserve your battery backup as soon as you loose power.. unlikey, but it's the only reason I could think of off the top of my head. The real gain in CPU scaling is seen on your laptop. You can really make a difference in your battery life by scaling down your CPU on your laptop.

The first thing you need to do is

cat /sys/devices/system/cpu/cpu0/scaling_available_governors

to see if your kernel has any cpu scaling governors built-in and loaded. If you don't see anything, or you get an error, try as root

modprobe acpi_cpufreq

If this command succeeds (no repsonse), then try the previous command again, but if you get an error, your kernel might not support CPU scaling and you might need to either upgrade your kernel or compile a custom one. Compiling a new kernel is beyond our scope in this meeting, but if your interested, let me know and we'll cover it in a future meeting.

There are some CPU scalers that are built into the kernel, these are: powersave, performance, conservative, ondemand and userspace. Powersave is always the lowest frequency, performance is always the highest frequency, ondemand and conservative both try to determine when CPU usage elevates and they elevate the CPU frequency and then they drop the frequency when the CPU usage goes back down. There is a small difference in the two, so look at this page for a quick explanation of the governors. The last governor, userspace, allows you to control the CPU frequency via userspace commands and scripts which we talk about next.