short answer: 4 pin 3 pin = fixed speed 4 pin = PWM fan, variable speed.
Hi All, I have bought an Aurora R12 and as with everyone else, the fans are a bit noisy.  I want to replace my fans but I am not sure if I should buy a 3 point or 4 point fan? I was going to replace 2 fans, one in the top and one at the front.  I was probably going to buy a Noctua. Thanks for your help,  
Aurora R12, fan