HP EliteDesk 800 G3 SFF Hardware Reference Manual page 23

Removing or installing an expansion card
The computer has two PCI Express x1 expansion sockets, one PCI Express x16 expansion socket, and one PCI
Express x16 expansion socket that is downshifted to a x4 socket.
NOTE: The PCI Express sockets support only low profile cards.
You can install a PCI Express x1, x4, x8, or x16 expansion card in the PCI Express x16 socket.
For dual graphics card configurations, the first (primary) card must be installed in the PCI Express x16 socket
that is NOT downshifted to a x4.
To remove, replace, or add an expansion card:
1. Remove/disengage any security devices that prohibit opening the computer.
2. Remove all removable media, such as compact discs or USB flash drives, from the computer.
3. Turn off the computer properly through the operating system, and turn off any external devices.
4. Disconnect the power cord from the AC outlet and disconnect any external devices.
IMPORTANT:
as the system is plugged into an active AC outlet. To prevent damage to internal components, you must
disconnect the power cord from the power source before opening the computer.
5. If the computer is on a stand, remove the computer from the stand.
6. Remove the computer access panel.
7. Locate the correct vacant expansion socket on the system board and the corresponding expansion slot
on the back of the computer chassis.
8. Release the slot cover retention latch that secures the slot covers by lifting the tab on the latch and
rotating the latch to the open position.
9. Before installing an expansion card, remove the expansion slot cover or the existing expansion card.
NOTE:
the expansion card.
Regardless of the power-on state, voltage is always present on the system board as long
Before removing an installed expansion card, disconnect any cables that may be attached to
Removing or installing an expansion card 17