Echo Express SE I (Thunderbolt 2 to PCIe Card Expansion System ...
PCIe 3.0 protocol standard: 4 PCIE slots include 2 PCIE X16 slots, 1 PCIE X4 slot and 1 PCIE X1 slot. The X99 motherboard supports the PCIe 3.0 protocol.
Máy trạm Workstation Lenovo Thinkstation P5 Tower ...
PCIe: Supports 6 PCIe slots with 2x PCIe 5.0 slots and 4x PCIe 4.0 slots; Storage: Up to ten drives (3x 3.5" SATA HDD + 7x M.2 SSD); USB Calliope Keyboard ...
NVIDIA H100 PCIe GPU
If you want to put an Arduino in a regular PCIe slot, you can use the SMBus lines, which are just I²C with additional constraints.