In any method of cooling you need a form of fluid to rush past the CPU to take the heat with it (convection cooling). With most computers the fluid is air blown by a fan over the heatsink. In those more adventurous overclockers looking for a reduction in temperatures, more speed or less heat water is used. This is more of a technical challenge since, as we all know, water and electricity don’t get along. For the most insane/rich/hardcore (delete as you see fit) overclockers out there there is Phase Change. Based on the same technology that keeps your milk cold in your fridge, it is capable of producing temperature well blow zero.