Sony VAIO PCV-R553DS Reference Manual page 45

Removing, Installing, and Replacing Components
5
If you do not replace the card or install another add-in card, install a
slot cover over the vacant slot at the rear of the chassis (see
an Open I/O Slot"
6
Replace the cover (see
on page 41).
"Replacing the Cover"
"Covering
on page 27).
31