Modern Central Processing Units (CPUs) consume a lot of power, which is converted to heat in the process. However, one of a computer’s worst enemies is heat. Heat can cause severe damage to any electronic component, especially integrated circuits (ICs).

Heat damage is not an issue for smaller electronic components, which do not generate enough heat to cause problems. However, CPUs, northbridge chips, and graphics cards all produce enough heat to destroy themselves if overheated. Early Pentium 1 computers had a serious problem with overheating, especially when used in a warm environment. This led to the installation of  heatsinks  and fans as standard items on computer CPUs.

The purpose of a heatsink or fan is to remove the heat from the CPU (or other chip) and dissipate it into the air. To do this, the heat first must be transmitted from the CPU to the heatsink. While this might seem like a simple enough proposition, it is not. Air makes a very effective heat insulator, so for the heat to get from the CPU to the heatsink, the heatsink must be installed without any air gaps whatsoever. Even an air gap of a few microns can slow down heat transfer.

Since it is virtually impossible to make a CPU and heatsink that fit together perfectly, a thermal paste or grease is sandwiched between the two. This non-conductive material is designed to fill any air gaps, ensuring the best possible mechanical connection between the two. The better air gaps are eliminated, the better heat flows out of the CPU and into the heatsink.

Heatsinks vs. Fans, vs. Heat Pipes

There are four basic ways of cooling a CPU: heatsinks, fans, heat pipes, and water coolers. Most systems use a combination of these methods, thereby enhancing the effectiveness of each. To make an informed decision when purchasing a CPU-cooling system, it helps to know how each one works.

Heatsinks

A heatsink is a metal object attached to the top of the CPU. It works by drawing heat away from the CPU itself and dissipating it into the air. Two factors determine how well a heatsink functions:

• Thermal conductivity
• Surface area

Thermal conductivity measures how easily heat can move through the material. For example, a metal spoon has a much higher thermal conductivity than a wood one. Thus, when a metal spoon is left in a hot pan, the heat travels from the end in the soup to the handle end, making it hot. However, a wood spoon sitting in the same pot of soup will not transmit the heat to the handle anywhere near as effectively.

Each type of material has its own specific thermal conductivity. Among metals, the highest thermal conductivity is found in silver, followed by copper, gold, and then aluminum. Since gold and silver are too expensive for making heatsinks, they are usually made of aluminum or copper.

Copper heatsinks are considerably better than aluminum ones because copper has a 70-percent higher thermal conductivity. However, copper is considerably more difficult to fabricate parts out of than aluminum. It is also much more expensive than aluminum, so more heatsinks are made out of aluminum than copper. Some aluminum heatsinks take advantage of copper’s higher thermal conductivity using a small copper pad that provides contact with the CPU.

To make heatsinks effective, they need a lot of surface area to be in contact with the air. This is why most heatsinks are designed with "fins" to create more surface area for transferring heat to the air around the heatsink.

A heatsink alone cannot provide enough cooling for modern CPUs. They need to be used in conjunction with a fan to increase the airflow over the heatsink’s surface area.

Fans

Fans cool a CPU by increasing the amount of air that comes in contact with the CPU. However, the thermal conductivity of air and plastic (the CPU’s case) are both about 0.1 percent that of aluminum’s. As a result, even though fans provide air movement, they do not provide enough heat transfer.

For a fan to effectively remove heat from a CPU, it needs to be used in conjunction with a heatsink. The high thermal conductivity and high surface area of the heatsink draw heat away from the CPU quickly and dissipate it into the airstream created by the fan. Most CPU fans are actually fan and heatsink combinations that are permanently attached together.

Heat Pipes

Any heat pipe system works in conjunction with a fan and heatsink. Heat pipes are liquid-filled copper pipes that connect to the top of the CPU and carry the heat away from it to a heatsink and fan. This is a highly effective cooling system, combining the most effective characteristics of three different technologies.

Heat pipes are very common in laptop computers, where there is not room to install a CPU fan. The heat pipe carries the heat away from the CPU, to the computer’s fan, which then helps dissipate the heat.

In desktop or tower systems, heat pipes are some of the largest cooling solutions available. However, they are more effective at drawing the heat from the CPU and dissipating it. The major concern when installing a heat pipe system, besides cost, is whether there is enough room within the computer’s case to mount the heat pipe.

Water Coolers

Water coolers are similar to heat pipes in that there is a liquid-filled tube going from the top of the CPU to a device which can dissipate the heat. However, rather than depending on the thermal conductivity of the copper pipe used in heat pipes, water coolers depend on the thermal conductivity of water. A large volume of water is moved constantly through the system loop, ensuring a high temperature differential between the CPU and the water being used to cool it.

A water cooler functions much like an automotive cooling system. The warmed water is pumped to a radiator with a fan blowing through it. The radiator is essentially a heatsink. The water-filled tubes allow the heatsink and fan to be moved away from the CPU to a place where they can be more effective.

Water coolers are the most expensive of any CPU cooling solution. They are also the hardest to install, so installation should not be attempted by a computer novice.

Comparing the Different Cooling Systems

In a side-by-side comparison of the various cooling systems, there are clear winners for both cost and cooling efficiency. However, not everybody needs the maximum possible cooling power. For most computer users, an average heatsink and fan will provide sufficient cooling. Power users who overclock their computers need the more powerful cooling options.

Type	Efficiency	Space Required	Cost
Heatsink alone	low	little	lowest
Fan alone	lower	little	low
Heatsink and fan	good	little to much	reasonable
Cooling pipes	high	can be much	a bit higher
Water cooler	highest	very much	highest

When selecting a cooling system for a computer, these three factors (efficiency, space, and cost) need to be taken into consideration. Buying a huge cooling pipe system that cannot fit into the computer’s case is not going to help anyone. On the other hand, not providing enough cooling can cause the computer to malfunction, or even cause damage to the CPU.

Selecting a CPU Fan and Heatsink Combination

In most cases, a CPU fan and heatsink are used in combination. The heatsink draws the heat away from the CPU, and the fan ensures a steady stream of air for the heatsink to pass the heat to. However, there is more to selecting a heatsink and fan than just looking for a good price or one that looks cool. The heatsink and fan must match the CPU, and most importantly, they must match the CPU socket.

The two major manufacturers of CPUs are Intel and AMD; everyone else’s CPUs are copies of one or the other. Together, Intel and AMD produce over 90 percent of the CPUs on the market. Their CPUs mount to different motherboards via different sockets and have different mounting solutions for the CPU heatsink and fan.

Computers that use an AMD CPU are easier to install fans and heatsinks to, as the CPU socket has tabs sticking out of two opposite sides for the heatsink and fan to clip onto. The fan is first clipped onto one side of the socket (usually the harder side to get to), holding the fan at an angle to facilitate attaching. It is then lowered to make contact with the CPU, and the other side is clipped on.

Intel’s CPU sockets do not have any integral mounting aids for the heatsink and fan. Instead, they are mounted through the motherboard, into holes in the four corners around the socket. Plastic snap-in pins are used to mount the fan and heatsink.

Each of these manufacturers produces several different CPUs that mount into different sockets. Between them, ten different sockets are currently in use. Therefore, it is imperative that the type of socket be known before buying so that a fan and heatsink that fit with that socket design can be purchased. In some cases, the names of these sockets are similar, so care must be taken when reading them.

Some fans and heatsinks are manufactured in such a way as to be compatible with a number of different sockets. If this is the case, the manufacturer will provide a listing of all socket styles that a particular fan is compatible with.

Conclusion

Since the creation of the first Pentium 1 microprocessor chips, it has been important to properly cool computers’ CPUs. Most computers have a heatsink and fan mounted directly to the CPU to accomplish this task. However, manufacturers typically use the least-expensive heatsink and fan they can find that will still provide adequate cooling. In cases where the computer is receiving heavy use, is overclocked, or is used in a warm ambient temperature, the CPU cooling system may need to be upgraded.

A CPU fan with an integrated heatsink is the most common way of cooling a CPU. While other fancier systems do exist, for most people, they are not necessary. However, for power computer users, especially for those who overclock their systems, a heat pipe or water-cooling system is essential.

Before shopping for a CPU cooling system, it is essential to know which type of CPU socket is in the computer. Not only are different sockets different sizes, but the mounting system differs depending on whether it is an Intel or an AMD computer. The heatsink and fan must be compatible with the processor socket.