ASUS P4B266-M motherboard user guide
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2.4.4 Connecting the CPU fan cable
When the fan, heatsink, and the retention mechanism are in place,
connect the CPU fan cable to the connector on the motherboard labeled
CPU_FAN.
3. Push down the locks on the retention mechanism to secure the
heatsink and fan to the module base.
When secure, the retention locks should point to opposite directions.
CPU Fan Connector
(CPU_FAN)