Dell Dimension U7021 Owner's Manual page 84

Installing a PCI Express Card
1 Follow the procedures in "Before You Begin" on page 67.
2 Press the lever on the card retention arm and raise the retention arm.
filler bracket
retention arm
84
Removing and Installing Parts
tab
lever
x16 card
x1 card
edge connector
card connector
top of retention
mechanism
securing slot
securing tab
edge connector
card connector