AMR and CNR Slots

Some motherboards have one of two specialized expansion slots in addition to the standard slots (PCI, AGP, and ISA) depicted in Chapter 4.

AMR and CNR riser cards are not sold at retail; they are generally sold by motherboard makers because they are customized to the design of particular motherboards. Although some parts suppliers sell AMR and CNR cards separately, it's best to get the riser card from the same vendor as the motherboard to ensure proper driver support.

The audio modem riser (AMR) slot (see Figure CD.2) enables motherboard designers to place analog modem and audio connectors and the codec chip used to translate between analog and digital signals on a small riser card. AMR slots are frequently found on systems with chipsets that integrate software modems (see Figure CD.3) and audio functions. However, very few AMR riser cards are available.

Figure CD.2. An AMR slot and PCI slot (left) compared to a CNR slot and PCI slot (right). Very few AMR riser cards were ever sold, but some mother board vendors bundle CNR riser cards with their motherboards to provide six-channel audio output and other features.

Figure CD.3. An AMR riser card used for soft-modem support (left) and a CNR riser card used for six-channel analog and digital-audio support (right).

The AMR has been largely replaced by the communications network riser (CNR) slot (see Figure CD.2), a longer design that can support up to six-channel audio, S/PDIF digital audio, and home networking functions. A number of vendors are using the CNR slot to implement high-quality integrated audio as shown in Figure CD.3.