BooneRebel has it mostly right....
My workstation has no internal HDs, just an external F/W hot-swap drive tower (Compaq).
My server has 4 drives internal in a hot-swap (that's the max) cage (which is in the tower, but the HDs (on sleds) can be pulled w/o opening the case up or powering the server down).
The server also has a 7 drive Fast/Narrow external hot-swap drive tower, which isn't full, because I can't find enough narrow drives, and I don't want to put in 1g drives.
And, I just bought another F/W drive tower, but this one's a rack-mount, and will take 7 drives. ($46.50 shipped from e*ay 🙂)