4 x 4 slot ✓ PCIe Gen4 x4 Slot - Adapter

4 x 4 slot 19 1He PCIe to PCIe Erweiterung with 4 PCIe x8 Gen-2 Slots Order-Nr : WM1-090-250, WM1-090-255 SeriesModel: ExpressBox4-1U-xG2, EB44 x 4 slot slot The system requires the PCIe bifurcation function to add more than one SSD with a full 16 lanes required for 3 or 4

4 x 4 slotUniversal AGP slot , 2 PCI slots , and 4 Compatibility; 5 Power consumption; 6 Protocol AGP command codes

4 x 4 slot Your assumption is correct This would be a slot with only four PCIe lanes connected, but it can fit a 16-lane card This is pretty common,