PCIe bifurcation

PCIe bifurcation splits the lanes of one PCI Express slot into several smaller links, each wired to its own device. A x16 slot can run as two x8 links or four x4 links, written x8x8 or x4x4x4x4. The split is a BIOS setting. It divides lanes the CPU already provides and adds none. Intel's desktop processor pages list the splits as PCI Express Configurations, and Supermicro's documentation tells you to bifurcate the slot.

Intel lists the Core Ultra 9 285K, a desktop processor, at 24 PCIe lanes with configurations of up to 1x16+2x4, 2x8+2x4 and 1x8+4x4. Supermicro's AOC-SLG3-2M2 carries two M.2 NVMe drives, and its FAQ says the second drive goes undetected with the slot set to 1x16 or 2x8. The fix is x4x4x4x4 or x4x4x8. A PCIe switch is the other way to put several devices behind one slot.

Read the board manual for the exact slot before buying a multi-drive carrier card, and confirm the split you need is listed. Intel desktop parts list allowed splits per processor, so check the CPU as well as the board. Its Xeon w9-3595X workstation page lists 112 lanes and no split table, which leaves the board manual as the reference there.

Sources

Last verified October 30, 2026.