What is the difference between a PCIe x16 slot and an express card

What is the difference between a PCIe x16 slot and an express card pcie x16 expansion slot Now for the question, I see lots of back panel USB cards for PCIe slots But can you plug that card into a PCI-Ex16 slot AND have it work? pcie cem slot Card capacity and size Mac Pro has eight PCIe x16* sized slots that accept many different types of PCIe cards: Slot 8 is x4 in size Mac Pro Expansion

pcie cem slot *Refer to com or this user manual for the Memory QVL Expansion Slots, 4 x PCIe x16 , support x16; x16x16; x16x8x8 and

pcie m2 slot Pi+® PCIE Expansion Card, PCI-E X16 to 2-Port NVME SSD PCIe x16 Slot, Gen3 Slot Personal Computer · ₹7,099₹7,099 P PCIe x16 slot, but expose two additional x8 slots One of the smaller slots should accept the HBA, while the other one