|3||Sense (Yellow or Blue): spin sensor|
Fans with three pin connectors Must Be Used on 3 pin CPU-Fan pinouts.
The #3 pin senses fan RPM (revolutions per minute). When no revolutions are sensed by the system, an audio alarm &/or no system boot will occur, warning the user &/or preventing proccessor overheating and burnout. Typically, the motherboard is required to pull the pin up through a resistor, with the fan connecting it to ground once (or more) per revolution.
Other 3 pin fan connectors, such as case fan connectors may use a fan with a 2 pin plug (12v+ & Gnd ). RPM notification is not important on those connectors.
No alarm or boot prevention is associated with these.