The most striking layout change resulting from the shrink from a 15" to 13" form factor is the rearranged battery cells. This allowed Apple's designers to cleverly tuck the SSD away underneath the trackpad assembly.

The empty space next to the SSD is very un-Apple. It's not like them to leave big air gaps in their newest, sleekest designs.

Our first thought was that a standard 2.5" laptop drive might fit in this space, and it almost looks like this little nook was designed with that in mind.

Our 9.5mm Crucial SSD didn't allow the bottom cover to be closed, but just by a smidge. We'll see if a 7 mm or 5 mm super-slim hard drive could be incorporated into the space.