Dell Dimension E521 - Manual (Page 26)

2. Align the drive panel tabs with the side hinges.
3. Rotate the drive panel toward the computer until it snaps into place on the front panel.
Drives
The computer supports a combination of these devices:
l Up to two serial ATA hard drives
l One optional floppy drive or an optional Media Card Reader
l Up to two CD or DVD drives
Connect serial ATA hard drives to connectors labeled "SATA0" or "SATA1" on the system board.
Connect serial ATA CD or DVD drives to connectors labeled "SATA2" or "SATA3" on the system board. See System Board Components .
Connecting Drive Cables
1 sliding plate lever 2 sliding plate 3 drive panel
4 drive panel tabs (3) 5 side hinges
1 CD/DVD
drive
2 FlexBay for optional floppy drive or optional Media Card
Reader
3 hard
drive