- There are standards that determine the pin-outs for interconnected components in PCs. There are only two standards for connecting the fans. The three-wire connection provides positive DC voltage, ground and fan speed. On the four-wire version, the fourth wire is for a speed control signal to the fan.
- The three-wire configuration includes a Molex connector to accommodate three wires. They are: black for ground, red for positive DC and yellow for the output tach from the fan. The tach line provides RPM information back to the computer.
- Most computers use the 4-wire configuration. This includes a fourth wire that provides a pulse width modulated (PWM) signal to the fan to control its speed. The fourth wire is usually blue.
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