8940 spec: ● Two SATA slots for 2.5-inch hard drive● One SATA slot for a 3.5-inch hard drive it is designed to support up to three sata devices. it provides One M.2 2230/2280 slot for solid-state drive/Intel Optane memory.    
I would like to install four(4) HDD in my XPS 8940. Two 2.5's and two 3.5's, but it seems to me to have only three SATA plugs for data cables on the motherboard. I realize that I will have to purchase an additional cable, but can't find a plug for it. please advise, cacheman
XPS 8940, four HDD, seems to be only three SATA plugs for data cables