Teardown: Dual-Switch PCIe Board Drives 8 GPUs From a Single x16 Slot

Developer Zach Mueller tore down and tested a GPU expansion board: it carries two PCIe switches, letting a host drive up to 8 GPUs from a single PCIe x16 slot, or even 9 in cascade mode. The board sells for around $4k.

Confirmed

• The board integrates two PCIe switch chips internally, the key to driving multiple cards over a single x16.
• Two wiring modes are supported: direct connection (two PCIe x16 to 4x x8 MCIO cables), giving each GPU independent bandwidth; or cascade (a single x16 splitting into 2x x8 MCIO), with further devices expandable via MCIO downstream.
• The same board can also be used for a lightweight configuration with 2 GPUs.

Why it matters

• This approach reduces multi-GPU deployments' dependence on motherboard slot count down to a single x16, a directly useful reference for building multi-card inference/training setups in workstations or compact cases.
• The two topologies, direct and cascade (including tested P2P topology), let users flexibly trade off between independent bandwidth and expansion scale.

2026-10-10 ~ 2026-10-10 · 8 related posts

• [source] One x16 slot, eight GPUs: how PCIe-switch expansion boards use direct-connect vs cascade topologies — TheZachMueller · 2026-10-10
• One $4k expansion board lets a single PCIe x16 slot drive up to 8 GPUs — TheZachMueller · 2026-10-10
• One x16 slot drives 8 GPUs: blogger to benchmark PCIe switch expansion board P2P topologies — TheZachMueller · 2026-10-10
• Dual PCIe-switch expansion board explained: 8 GPUs off one x16 slot — TheZachMueller · 2026-10-10
• [source] Distributor clarifies 8-GPU PCIe expander: no slapping a 9th GPU off one slot — TheZachMueller · 2026-10-10
• [source] Keeping the cascade GPU setup requires another direct plus a retimer — TheZachMueller · 2026-10-10

2 near-duplicate retellings: TheZachMueller · TheZachMueller