I'm sorry if this has been answered before, I did try searching several different ways and found no help. I recently purchased HDadvance and all the required components... I plan to fill the hard drive up fairly quickly and then would like to purchase another hard drive. I figure I'll get another Maxtor as this one seems to work great. My only question is... what's the difference between 3.5" and 3.5" X 1/3H ? Which will fit, or will they both?