Both ends are identical so it doesn matter which one end you plug into the Mobo however look at the slots on either side of the mobo plug and make sure you line them up correctly. The side guides only fit one way correctly. The DVD Drive plug must also go in the correct way or you will fry your drive. The half with more room above the side guide goes on top (1/4 " above the side guide goes on top and the 1/8" below the guide is on bottom). I like to put a black line on mine so I can quickly identify which way it should plug in. If this isn't clear I'll take a photo and send to you on email.