Processor Cooling Basics
It's important to know a few basic facts about processor cooling. All desktop processors available today are pretty easy to handle, as the actual processor die is protected by a large metal plate covering the entire upper part of a processor. This metal plate is called the heat spreader, as it provides a larger footprint for dissipating heat from the processor to the heat sink. It also protects the processor die from physical damage, such as might occur if you install a heat sink without taking sufficient care.
Processor heat dissipation depends on the processor architecture - Core 2 is much more energy efficient than the older Pentium 4 or Pentium D. The number of processing cores is also a factor, since a dual core will always require more energy than a single core, as is the clock speed at which the processor runs. The higher the clock speed, the more voltage has to be applied, which also causes increased power consumption. Power requirements increase exponentially as you increase either parameter.
Classic air CPU coolers differ in terms of size, layout, material and the fan type and size. Heat sink size, layout and material correlate greatly, as the issue is all about conducting as much heat as possible away from the hot spot onto a metal surface that is as large as possible. This is why efficient heat sinks will have lots of thin fins and use copper where possible: the metal heats up, and an air flow created by a fan is used to blow the hot air away from the cooler. Copper is much heavier than aluminum, which makes it somewhat tricky to build a full-copper heat sink.
Processors are often sold with a boxed cooler and fan. Today's coolers are efficient and quiet, and they will be sufficient if you don't intend to overclock your processor. Go for an aftermarket cooling solution if you want more cooling performance, though.
There are several possible points of failure for processor coolers, the first obviously being installation. Always make sure that you either use the included thermal pad or thermal compound. Use as little compound as possible, as it only has to ensure airtight contact between the CPU heat spreader and the heat sink. If the compound comes leaking out at the sides so that you have to remove it, you used too much.
As you install the heat sink, pay close attention to the installation. The surface has to sit on the heat spreader evenly. If you're using a sophisticated aftermarket CPU cooler, it will probably have an efficient layout and provide basic heat dissipation for most desktop systems. However, the fan is required as soon as the CPU is actually used and placed under a higher load, which brings us to the point of failure we've looked into: every fan is a mechanical device with a limited life span. As the fan fails, the cooler will not be able to remove all the heat dissipated by the processor.