The PaQ 4U-550 has been designed so that it can be used as either a MidiTower or as a RackMount, or indeed as a DeskTop.

For a RackMount you will need the Optional RackMount Brackets; but no other differences exist.

The Self-Adhesive Acoustic Feet can be attached to work in either Midi Tower or Desktop mode.

The reason this is possible is that the External Drive Bay for CD/DVDs and Floppies is square, so the drives can be installed in either orientation. Packing Pieces are provided as standard with the PaQ 4U-550. They support the drives and fill in the empty space.