The internal 3.5" drive bay can fit 4 hard drives when using the removable drive trays, and 3 when using Antec's hard drive suspension mechanism.
Antec's hard drive suspension mechanism is quite simple. It consists of two loops of elastic fabric in which you pass your hard drive through. The drive is then suspended in these loops. This is a great way to absorb hard drive related vibrations, and insulate them from the whole case. As a warning though, the drives can slide out if the case is tilted too far.
Three pairs of these loops are installed in the case, so this limits you to three hard drives if you opt to mount this way.
The Sonata Plus also includes another method of mounting internal 3.5" drives, using trays fitted with rubber grommits. While not as effective in insulating vibrations as the elastic drive suspension mechanism, it's quite a step up from making full metal-to-metal contact between the case and hard drive.
The interior case layout is fairly typical. The power supply is at the top-rear corner, all drive bays at the front, and the motherboard tray taking up the rest of the case. The motherboard tray is the size of a full ATX motherboard, and also accepts mATX motherboards.
A bar goes accross the length of the case to help the case maintain ridgidity. Less vibrations means less noise. All of the steel edges inside the case are folded, so there are no sharp edges. The Sonata Plus is very safe to work with internally.
The Sonata Plus case comes packaged with Antec's Neo HE550 power supply. It's a modular power supply with active PFC. circuitREMIX will be examining this power supply in greater detail in a future review.