looks like it may hold even more than 4... if the bottom slide out frame thing is 4 x 3.5" bays (sideways?) + 3 x 3.5" in the middle box + 2 (possibly 3) x 5.25" bays = 9??

Or i may be slightly wrong..

Thats a lot of HDDs

 

The middle box holds two and the lower box four.
The only difference with the lower four is they're held sideways by rubber grommets to reduce vibration.

 

Oh that's hot. New case, here I come! Thanks guys.