Hi, I'm building up my own pc and this is my first time to do so. My motherboard is Gigabyte GA-MA785GM-US2H. So I have connected everything apart from the socket for SYS_FAN and NB_FAN. I actually forgot to buy the case fan(the one below PSU), so now I'm now confused to buy which kind of fan for SYS_FAN and NB_FAN. Is NB_FAN actually necessary ? My SYS_FAN has 4 pins and for NB_FAN it has 3 pins.