The cable with two 'large' 4-pin connectors is for your hard drive(s). The one(s) with the smaller 4-pin connections for the floppy along with the larger drive plugs are for the floppy, CDROM/DVD(s), and fans. The one with the little square 4-pin connector (usually with 2 yellow and 2 black wires) is for supplementary mainboard power, as is the one with 3 orange and 3 black wires that looks like an old-style AT mainboard power connector. Not all MBs take these connections. If you have a connection that looks like the ones you pluged into the hard drives but with only a yellow and one black wire to it, that one is exclusively for fans.
