There are four (4) more screws holding the bottom panel on the PC-O5s.
The front and back pieces are both also held in place by screws. Have I mentioned yet that I’m really glad it’s all screws and not rivets?
The PC-O5s also comes with a PCIe x16 3.0 flexible riser cable.
On the back side of the motherboard tray, there is a bracket to install a slim optical drive on.
There are also holes to mount a 2.5” drive to the optical drive tray.
Continuing on with more hidden storage, there is a removable plate on the back of the motherboard tray that can hold either one (1) 3.5” drive and one (1) 2.5” drive, or two (2) 2.5” drives.
There are also mounting holes for either two (2) more 2.5” drives, or a 2.5” and a 3.5” drive on the front (but using a 3.5” drive will mean losing the PCIe slot). There are also holes that should be for mounting a second 3.5” drive (on the left), but the rear I/O panel gets in the way.
There is a drive cage that can hold an additional three (3) 3.5”, and a single 2.5” drive. They also include a cover that mounts on the top hard drive, to cover it up. Another nice touch to keep the inside looking nice and clean.