Since the earliest form factors, computer cases have included a number of expansion
slots (see Figure 15-18) that can be used to add ports or functions such as sound cards,
video cards, video capture cards, scanner controller cards to the PC. The ports for these
types of devices are not included in the form factor definition because it is very difficult to
predict how each user wants to configure their PC in terms of its peripheral devices. The
numberofopenexpansionslotsvariesbyformfactor.Whenchoosingacaseforyourpro-
ject, be sure to examine the specifications to determine which best meets your needs.
When you wish to use an expansion slot and extend its port through the case, the slot
cover is removed to expose the case slot. However, when an expansion slot is not in use, it
should be covered. Many cases do not come with slot covers to close their unused expan-
sion slots, so be sure you ask for them or have some on hand.
Acurrenttrendamongcasemanufacturersistoleaveapunch-outorknockoutslugin
the I/O ports on the I/O template and the expansion slots (see Figure 15-19). If you are
not using a port or slot, you can leave the slug in place. However, be sure you understand
how this affects the case cooling before assuming it is a part of the overall case design.
Chapter 15: The System Case^361
Figure 15-18. The location of I/O ports and expansion slots on an ATX mid-tower chassisI/O portsExpansion
slots