riser card

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riser card

(1) A printed circuit board for low-profile motherboards. The peripheral controller cards plug into the riser card and sit parallel with the motherboard. See low-profile motherboard.

(2) An expansion card that is used to physically extend a slot in order to make it easier to plug in the chip or card.

(3) A small PC expansion card that contains audio, modem and networking capabilities. When first introduced, it let manufacturers create custom systems for different audiences using motherboards that had none of these built-in functions. After audio and networking were built into the motherboard, risers were used for modems because they could be easily interchanged for international certification (homologation). See AC'97 and HD Audio.

Audio/Modem Riser (AMR)
AC'97 Audio, V.92 Modem
In 1998, Intel introduced software-driven audio and modem capabilities in the 46-pin AMR card as well as a Mobile Daughter Card (MDC) for portable solutions. Although motherboards were built with AMR slots, AMR offered little because it usurped a PCI connection, lacked Plug and Play and was software driven.

Communications and Networking Riser (CNR)
AC'97, V.92, Ethernet, HomePNA, USB
In 2000, Intel introduced the 30-pin CNR card, which added Plug and Play support and audio, modem and network functions. CNR included USB and took up one PCI slot. Ethernet and HomePNA connectivity was provided via the Intel LAN Connect Interface (LCI) or the Media Independent Interface (MIL).

Advanced Communications Riser (ACR)
AC'97, V.92, Ethernet, HomePNA, DSL
In 2000, AMD, 3Com and others introduced ACR to supersede AMR. Taking up one PCI slot, it accelerated audio and modem functions in hardware. For audio and modem only, it could be built with a connector to plug into an AMR slot. For networking, the card used a full PCI slot, colored blue and reversed.

ACR allowed modem, HomePNA and DSL to be connected over one telephone jack. It also supported multiple Ethernet controllers.

PC Motherboard Riser Cards
ACR cards can be designed to fit into AMR slots or PCI slots (blue and reverse from standard PCI).
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