Supermicro SAS Breakout Cable

[Opty1218]

I was looking at Supermicro boards with onboard SAS and saw they came with bundled breakout cables that look like this:

I know it's supposed to be a 4 sas/sata breakout, but what is that extra grey cable for? the one labeled "p4" ?

 

[xnoodle]

It's the sideband cable. You can connect it to compatible hardware for communication between the backplane and the controller. You don't need it to be plugged in, you can leave it dangling typically if you're using backplanes/chassis with no sideband connector.