PCIe riser cables

PCIe riser cables are flexible extensions that relocate a motherboard's x16 slot, primarily used to enable vertical GPU mounting or manage component layout in Small Form Factor (SFF) chassis.

Riser cables act as a high-bandwidth bridge, extending the PCI Express slot to allow for non-traditional component placement. Their primary function is facilitating aesthetic vertical GPU mounts or enabling compact builds (SFF PCs) where a direct motherboard connection is impossible. Modern cables must meet stringent specifications: a quality PCIe 4.0 riser, for instance, maintains the full 32GB/s bidirectional bandwidth to prevent performance loss on high-end cards like the RTX 4090 or RX 7900 XT. Using a lower-spec cable (e.g., a Gen 3.0) with a Gen 4.0 or Gen 5.0 system requires manually downclocking the slot in the BIOS, a critical step to avoid stability issues or boot failures.

https://www.overclockers.co.uk/blog/pcie-4-0-riser-cables-everything-you-need-to-know