Two computers ago, or maybe three, I bought my computer built to spec from a local computer shop. I configured my computer through their website, and one of the options was for thermal compound, which they described as improving the cooling solution of the system. It was only a few bucks if I decided to get it, and of course I didn't think anything of it at the time, so I added it to my order.

Since then I have found out that thermal compound, also known as thermal grease, is really not optional. If you've ever taken apart a computer or server, and found the heat sink practically glued to the CPU by some gunk, to use a technical term, that's thermal grease.

Thermal grease ensures that there's no gaps between the heat sink and CPU, so heat is transferred from the entire surface of the CPU. If you were able to look at the surface of a CPU and a heat sink at the microscopic level you would see that they're not perfectly even. There's hills, valleys, ridges, ruffles...no, forget that last one. Any place where one surface is away from the other because of one of those valleys or such is a place where heat is not going to be transferred as efficiently as possible. Thermal grease gets down in all those spaces and fills them in. Because it's thermally conductive, it ensures that heat gets taken by the heat sink from the entire surface of the CPU, and no hot spots develop. It's not an optional step. It's a mandatory one, to make sure your system works properly.