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What is a CNR Slot in a Motherboard and Its Relation to Riser Cards

November 21, 2025


A CNR (Communications and Networking Riser) slot is a specialized expansion slot found on certain older motherboards, primarily from the early 2000s. Its main purpose was to provide an economical and flexible way to add networking, audio, or modem capabilities to a PC without requiring full-size PCI cards.

How it works:

  • The CNR slot connects to a riser card, a small card that “rises” from the motherboard and holds additional components.
  • Instead of inserting multiple full-sized PCI cards, a single riser card could provide Ethernet, audio, or modem functions through the CNR slot.
  • This setup saved motherboard space, reduced costs, and simplified PC assembly.

Relation to riser cards:

  • The riser card is the physical device that plugs into the CNR slot.
  • It effectively “extends” the motherboard’s functionality in a compact form factor.
  • This is similar in concept to network risers in buildings, which provide structured pathways for multiple connections, but at the PC component level.

Key point:
CNR slots are mostly obsolete today, replaced by integrated motherboard features or standard PCIe expansion slots, but they were an early solution for modular and flexible connectivity in PCs.

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