Fundamentals of air cooling
It is normal for electronic components to warm up as current passes through. However, they need to be protected from overheating - this is achieved by simple air cooling. Designers came up with the ATX specifications for cases and components, which also takes in consideration the placement of heat-generating circuits and how airflow will cool them all. There is a reason why cold air enters from the front and bottom of the case, flows around all components absorbing heat and finally is exhausted through the power supply at the top and rear. It is a bad idea to run the computer with the case open; the internal airflow is gone, and even if you think that components will be cooled better in the open case - they’re not: hot air right above the circuits is no longer moved by fans, so components overheat.
Processors are by far the biggest heat generators in a computer. They need adequate cooling to take heat from the processor and transfer it to air. This is done by heatsinks. There are two elements of interest here: the material of which the heatsink is built, and the contact surface between the metal and air. First of all, full-copper heatsinks are heavier and more expensive than aluminium ones, but they provide a better transfer of heat from the processor to the base metal plate and from metallic fins to air. Note that because of the weight, some coolers for AMD processors will need to be attached to the motherboard with screws rather than clamping them to the plastic CPU socket, so make sure your motherboard model has the mounting holes and the space around the socket for that specific heatsink; all modern Intel motherboards have a standard system to attach the heatsinks to the motherboard. Secondly, the largest the compound surface of all metallic fins, the better will heat be transferred to air, so look for heatsinks with many, thin, large surface fins. Manufacturers will try to trick you with all kinds of stuff: aluminium heatsink with copper insertion where it touches the processor, or cyllindrical shaped heatsinks, or other weird stuff; I’m not saying these solutions are not working, but I’d rather use a large copper heatsink, such as the ThermalRight SP-97 for AMD AthlonXP processors.
Air needs to be ventilated through the heatsink continuously by a fan. The more air passes through the heatsink, the more heat it will absorb from the metallic fins. The key here is the volume of air. Since fans come in several sizes, usual dimensions being 40, 50, 60, 80, 92 and 120 milimeters, you can get the same volume of air pushed through with a small fan at high speed or with a large fan at low speed. The heatsink will accomodate only one or a few sizes of fans, though, and that might be a little restrictive sometimes. Many CPU cooling kits include a heatsink and a fan, but you might consider replacing the fan with a better one of same size, or just buy them separately for more flexibility. The problem here is that fans make a horrible noise at high speeds; you might not hear them at 2000 rpm (revolutions per minute), but at 4500 they’ll scare your neighbour’s cat. To move the same volume of air through the heatsink while keeping noise to a minimum, the best solution is to attach the largest fan you can mount on the heatsink; pick one which runs at lower speeds or get a variable fan speed controller. Some CPU coolers have temperature sensors; they’re not that great, and they will only run at minimum specified speed when the computer starts up cold - afterwards, temperatures jump up quickly inside the case. Ball bearing fans are quieter and more reliable than sleeve bearing ones, but they still need to be cleaned as often as needed to prevent vibrations and noise.
Some cooling specialists consider that it’s not too efficient to have the CPU cooler recirculate the warm air inside the case through the heatsink, and they suggest using a case with a special opening in the side panel so the CPU cooling fan draws cool air directly from outside. Others claim that the difference is insignifiant. If you are into case modding or extreme cooling, perhaps you should give this idea some thought.
Airflow inside the case is usually assured by the fan inside the power supply. Recently, power supplies with huge 120 milimeter fans appeared on the market - these will provide a very good airflow at slow speed (1200-1800 rpm) thus being very quiet. Other power supplies have two or even three regular 80 milimeter fans; doubling the number of fans doesn’t necessarily improve airflow, but adds noise. Finally, a few power supply models have temperature-controlled fans which run at different speeds based on air temperature - this is probably a good choice for most people.
If you don’t have a power supply with an oversized fan, it is a good idea to supplement airflow by mounting an exhaust fan at the back of the case, if it can be done. Again, keep in mind that larger fans at lower speeds are quieter while having the same results as smaller but faster (thus noisier) fans. Mounting a supplemental 120 or 92 milimeter fan at the back of the case is excellent.
If your case doesn’t have many air vents on the sides, it is usually a good idea to match or slightly exceed the exhaust fans’ total volume of air displaced with an intake fan mounted at the front of the case. This will prevent air and dust from being sucked in through every possible hole, even through the floppy drive slot and around the CD tray opening. If possible, pick a case which allows mounting a 120 milimeter fan at the front and also protect it with a replaceable, washable air filter.
A few people decide on replacing air cooling with liquid cooling. Basically, heat from the processor and graphic card is absorbed by liquid instead of air, then the liquid is cooled through a radiator mounted at the back of the case. This solution can be a lot more expensive than air cooling, not signifiantly quieter, and still needs the other components in the computer to have a minimum airflow.
The second source of heat in the system is the video card’s graphic processor. Often overlooked, this small fan can be the source of a loud, high-pitched noise. Luckily, there are solutions for replacing the heatsink and fan with better ones, both in terms of cooling as well as less noise producing.
The third source of heat is your hard drive. It heats up from spinning at high speeds, and the last thing you want to do is risk losing your data by cramming a bunch of hard drives together or placing the hard drive in the empty bay next to the floppy drive. Instead of adding one of those inefficient hard drive coolers (another fan in the case, another source of noise), look for a case with a rail of 3.5″ bays at the bottom, able to accomodate 5 to 8 hard drives. Mount your hard drive somewhere in the middle, where it will be cooled by the air coming in the case through the front vents (and possibly front intake fan) and it should run happily for years. Tests also indicate that a good contact between the hard drive case and the metal of the computer case helps it cool down and also prevents electrostatic charge from accumulating and zapping your data, so you might consider a good old-fashioned screw mount than plastic rails or rubber spacers between the hard drive and the case. Some people came up with a solution of suspending the hard drive with elastic cords to prevent vibration from being transmitted to the case; they overlooked the electrostatic charge problem because the hard drive was no longer grounded, and data corruption occured more often than usual.
