Fans are a requirement whether an air-cooled rig is being built or if a more advanced PC water cooling is being installed. Processors, in particular, can get hot so a Cooling Fan Hub does the work of cooling it. In most PCs, one or two fans, along with the GPU fan, are sufficient to keep the PC cool. All the fans plugged into the hub must be 4-pin type (PWM Control Mode). The reason being is that hub cannot exercise any speed control over 3-pin (Voltage Control Mode) fans. Most of the mid-range motherboards usually have a fixed number of 3-pin case fan connectors and 4-pin PWM connectors on them. So, in order to install more case fans in the PC case then a Fan Hub will be required and in order to control their speeds, a Fan Controller will be required. A fan hub permits the connection of more fans using a single power connector (generally 4-pin Molex or SATA connector) whereas a Fan Speed Controller allows to add more fans and the speed can be changed individually.