Linux-PHC (Linux Processor Hardware Control) is a patch for the Linux kernel
that provides a userspace interface to control the core voltage of a computer processor(s).
The main use of this interface is to lower the core voltage of a laptop's CPU ("undervolt").
The goal is to reduce the laptop's temperature so the cooling fan can safely run at a slower speed.
Another goal of undervolting is to reduce the power consumption of a laptop and thus extend its battery lifetime.