The ROUND ONE is called a Molex connector.
by R. Proffitt
- 4/27/12 4:27 PM
In Reply to: Computer Fan connector difference question? by JFCreally
Yes I could get all technical on you but that one is so you can tap power from the usual ATX power supply.
The square one looks to be the rare 4 pin that has RPM and possibly temperature sensing.
I won't discuss the latter without full details on the host PC.
Bob

Moderator
CNET Staff
Samsung Staff
Dell Staff