Every 2 USB ports are connected to a USB header, be it 1.0,2.0 or 3.0, A USB header is where the connection between every USB port Takes place (except the original ones in the back of the Mobo)
so basicly it is like plugging a internal HDD through a USB cable.Using the adapter I uploaded, The header will split up into 2 usb ports, which another adapter turns a single port into a SATA connection and then you can plug your HDD in
the PCIE one is much neater, but will need a PCIE slot that isnt being used (the small one) basicly it turns the pcie output into 1or2 SATA inputs, this is essencialy like adding another 2 SATA connections to your motherboard, just in another part of it