Most all modern computers contain at least one mechanical fan to keep internal parts like the processor, power supply’s and graphic cards from overheating from the heat they generate. Fans come in many sizes, colors, features and styles. The larger fans can spin slower than a smaller fan providing similar air flow output. Smaller fans are generally louder in sound due to there high speeds required to make up for their small size.
The performance and longevity of a fan is most often dictated by the cost. Bearings on inexpensive units can be a simple sleeve bearing as opposed to the more costly ball , fluid and magnetic style bearings.
Air pressure and Air flow are the most important two factors when choosing a fan to displace or move heat. Air pressure is rated in mmH2O and air flow is measured in cubic feet per minute (CFPM)
Computer Fans are Keeping Things Cool – Ask a Tech #33
All about computer fans but were afraid to ask.