Adapter cards increase the functionality of a computer by adding controllers for specific devices or by replacing malfunctioning ports. Figure 1 shows several types of adapter cards, many of which can be integrated into the motherboard. These are some common adapter cards that are used to expand and customize the capability of a computer:

Computers have expansion slots on the motherboard to install adapter cards. The type of adapter card connector must match the expansion slot. The different types of expansion slots are shown in Figure 2.

A riser card was used in computer systems with the LPX form factor to allow adapter cards to be installed horizontally. The riser card was mainly used in slim-line desktop computers.

Communications and Networking Riser (CNR) is a special slot used for some networking or audio expansion cards. The CNR is not in use any more because many of the functions of the CNR are now found on-board the motherboard.