Dell Vostro 400 (Mid 2007) - Manual (Page 19)

Setting Up and Using Your Computer
19
CAUTION:
Ensure that none of the system air vents are blocked. Blocking the
vents would cause serious thermal problems.
5 card slots Access connectors for any installed PCI and PCI
Express cards.
6 padlock rings Padlock rings are for attaching a commercially
available theft-deterrent device. The padlock rings
allow you to secure the computer cover to the
chassis with a padlock to prevent unauthorized
access to the inside of the computer. To use the
padlock rings, insert a commercially available
padlock through the rings, and then lock the
padlock.
7 security cable slot Security cable slot lets you attach a commercially
available antitheft device to the computer. For more
information, see the instructions included with the
device.