Compaq EN Series Hardware Reference Manual page 14

2-6 Hardware Upgrades
7. Before you install each drive into the chassis, turn it so that it is
perpendicular to the internal 3.5-inch drive. The bottom of the
drive should be parallel to the green drivelock.
The diskette drive should always be placed in the bay nearest
the top of the chassis in the desktop configuration for proper
drive clearance and access.
Installing a Drive in the Desktop Configuration
8. Gently slide the drive into the bay. When the drive is properly
inserted, the drivelock will secure it.
CAUTION: The use of unnecessary force may result in damage to
the drives.
9. Reconnect all power and data cables to the drives in the 5.25-inch
drive bays.