EDIT: They are PC fans.
In: Technology
More expensive, and the efficiency in terms of wattage isn’t really a big enough deal.
The biggest benefit to 4-wires isn’t efficiency (there’s plenty of other spots in a computer using many more watts than a fan that can be improved, to say nothing of the recent fad for packing fans with RGB LEDs), it’s that they can be slowed to be quieter.
The fourth wire is used to vary the speed of the fan. This is useful for things like CPU fans that would want to ramp up and down according to need. Lower power consumption fans that don’t have need to change speed such as case exhaust fans are fine with just three wires and no ability for their speed to be controlled, and so can be slightly less expensive to produce.
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