Case fan

Used to aerate the case of the computer. The components inside the case which use active cooling cannot remove heat efficiently if the surrounding air is too hot. Case fans move air through the case, usually drawing cooler outside air in through the front (where it may also be drawn over the internal hard drive racks) and expelling it through the rear. There may be a third fan in the side or top of the case to draw outside air into the vicinity of the CPU, which is usually the largest single generator of heat. Case fans are usually 80 mm or 120 mm along each side. Because case fans are often the most readily visible form of cooling on a PC, decorative fans are widely available and may be lit with LEDs or made of UV-reactive plastic. Decorative grilles are also common. Decorative fans and accessories are popular with case modders.


PSU fan

PSU fans often play a double role, not only keeping the PSU itself from overheating, but also removing warm air from inside the case. Many modern PSUs expel the air from the rear, but only from the PSU itself. PSUs with two fans are also available, which have a large fan on the bottom for removing case air and a smaller one on the back for expelling the warm air at a faster rate.



CPU fan

Graphics card fan

Used to cool the GPU and/or memory on graphics cards. These fans were not necessary on older cards because of their low heat dissipation, but most modern graphics cards, especially those designed for 3D graphics and gaming, need their own dedicated cooling fans. Some of the higher powered cards can produce as much heat as or more heat than even the CPU (over 140 watts), so efficient cooling is especially important.


Chipset fan

Used to cool the northbridge of a motherboard's chipset or for system bus overclocking.



Other fans

Other less commonly encountered fans may include:

* PCI slot fan: A fan mounted in one of the PCI slots, usually to supply additional cooling to the PCI and/or graphics cards.

* Hard disk fan: A fan mounted next to or on a hard disk drive. This may be desirable on faster-spinning (e.g. 10,400 RPM) hard disks where heat production is higher.



Physical characteristics

The width and height of these usually square fans are measured in millimeters, with common sizes including 60 mm, 80 mm, 92 mm and 120 mm. The amount of airflow which these fans generate is measured in cubic-feet per minute (CFM), and the speed of rotation is measured in revolutions per minute (RPM). Often, computer enthusiasts choose fans which have a higher CFM rating, but produce less noise (measured in decibels, or dB), and some fans come with an adjustable RPM rating to produce less noise if the computer does not need much airflow. Fan speeds may be controlled manually (a simple potentiometer control, for example), by the computer hardware or by software.

The type of bearing used in a fan can affect its performance and noise output. Most computer fans use one of the following bearing types:

* Sleeve bearing fans use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings can fail at higher temperatures, and may perform poorly when mounted in any orientation other than horizontally. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50°C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings.

* Ball bearing' fans use a sealed bearing containing steel balls against which the axle rotates. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, can endure higher temperatures, produce less noise and are more durable. The lifespan of a ball bearing fan may be around 63,000 hours at 50°C.

* Fluid bearing fans have the advantages of silent operation and high life expectency (comparable to ball bearing fans).