They tried that. Quantum made the quarter-height 5.25" "Bigfoot" drives for a little while. They didn't go far. I think the problem is that a larger disc, th

They tried that. Quantum made the quarter-height 5.25" "Bigfoot" drives for a little while. They didn't go far. I think the problem is that a larger disc, though it has greater area, also comes with worse mechanical stresses, plus the head has to be larger, which again means greater mechanical stresses and distortion under movement, and can't seek as quickly. There's a reason drives have gotten steadily smaller; otherwise they'd be making big, flat 8" or 12" hard drives for really high-capacity needs.