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Communications and networking riser

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CNR slot

Communications and Networking Riser, or CNR, is a slot found on certain PC motherboards for specialized networking and telephony equipment. A motherboard manufacturer can choose to provide audio, networking, or modem functionality in any combination on a CNR card. CNR slots were commonly found on Pentium 4-class motherboards, but have been generally obsoleted in favor of on-board or embedded components.

Physically, a CNR slot has two rows of 30 pins, making 60 pins total. There are two possible pin configurations, Type A and Type B. Both have 60 pins, but each has different pin assignments. CNR Type A uses 8-pin network interface, while Type B uses 16-pin MII bus LAN interface. Both types carry USB and AC'97 signals. A CNR slot is often brown in color, and is usually located in the lower-left corner of the motherboard.

Intel developed the CNR slot to replace its own AMR technology. Two advantages over the AMR slot it replaced are that it can be both software based (CPU-controlled) or hardware accelerated (dedicated ASIC), and that CNR is plug-and-play compatible. On some motherboards, a CNR slot replaces a PCI slot, but many motherboard manufacturers engineered boards that allow the CNR and last PCI slot to share the same space.

Just as with AMR, CNR has the potential for cost savings for motherboard manufacturers by removing analog I/O components from the motherboard. This allows the manufacturer to certify with the FCC only the CNR card, and not the motherboard. This, in turn, results in a quicker time to market for new motherboards, and allows mass-production of CNR cards to be used on multiple motherboards.

The Advanced Communications Riser (ACR) slot is a competing specification developed by a group of third-party vendors. Its principal advantage over CNR is that is uses a backwards-compatible slot layout that allows it to use both AMR and ACR cards. The same group also developed a physically smaller version, the Mobile Daughter Card, which is otherwise identical.

See also

  • AMR, the original Audio/Modem Riser that CNR replaced
  • ACR, a 3rd party solution to the CNR problem
  • MDC, a version of ACR for mobile devices
  • GeoPort, a similar standard for the Apple Macintosh


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