Dell XPS 8500 (Early 2012) - Manual (Page 48)

Postrequisites
1 Replace the graphics-card bracket, if applicable. See "Replacing the
Graphics-Card Bracket" on page 36.
2 Replace the computer cover. See "Replacing the Computer Cover" on
page 25.
3 Follow the steps in "After Working Inside Your Computer" on page 15.
PCI-Express x1 Card(s) 48