To the right of the motherboard compartment are six trays for 3.5” HDDs. Each tray is a separate rack for a single HDD. Once the HDD/ODD compartments are unlocked, you can remove the rack by simply sliding it out from the rack. Each tray can also hold a 2.5” SSD drive instead of the 3.5” drive if you have one of the latest drives.

HDD Racks

HDD+SSD

Side of SSD

Side of Raptor HDD
Once the 3.5” bay is out of the rack simply slide the 3.5” drive into the rack and screw it in. The back of the drive is facing the open end of the rack so you can insert the SATA Data and Power cables. The 3.5” drive bay can also mount 2.5” SSD drives. The 2.5” drive is mounted on the inner rack of the tray. Simply mount the drive on the tray and screw it in from the bottom and your SSD drive is installed exactly like the 3.5” drive is.
 HDD rail
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 HDD installed
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