CPUFreq is a Linux kernel subsystem which allows the clock speed of mobile CPUs 
(most often found in laptop computers) to be explicitly set. CPUSpeed 
dynamically controls CPUFreq, slowing down the CPU to conserve power and reduce 
heat when the system is idle, on battery power or overheating, and speeding up 
the CPU when the system is busy and more processing power is needed. Using 
CPUSpeed can significantly increase a laptop computer's battery life and 
significantly reduce the heat it generates while still allowing your system to 
perform at top speed when you need it.