HP DC5100 Hardware Reference Manual page 22

Hardware Upgrades
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7. Install the expansion card by sliding the card under the slot cover
retention latch then pressing the card down into the slot on the
system board.
Be sure not to scrape other components in the chassis when installing
an expansion card.
Installing an Expansion Card
8. Rotate the slot cover retention latch back in place to secure the
expansion card.
When you install an expansion card, make sure the metal bracket on
the card slides into the slot on the back of the computer then press
down firmly on the card so that the whole connector seats properly in
the expansion card slot.
CAUTION: All expansion card slots on the rear of the computer must
contain either an expansion card or slot cover for proper cooling of
internal components during operation.
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