can i put a pcie 4.0 in a 3.0 slot - Can I Use a PCIe 3.0 Card in a 2.0 Slot? - PC Guide 101 slot mega 888

Slot Type Size (Pins) Common Use Mini PCI 100 or 124 Wireless cards Mini PCIe 52 SSD storage, wireless cards. ... Yes, PCIe is backward compatible, so you can use a PCIe 3.0 card in a PCIe 4.0 slot without issues.

Will I be able to get all 3 PCIE cards to work, or can I assume that the 2nd PCIE 3.0 x8 can't fit in a PCIE 4.0 x4 (in a x16 size).

Can I Use a PCIe 4.0 Graphics Card in a PCIe 3.0 Motherboard Slot? ... You can use PCIe cards of a lower lane width (e.g., x2, x4, or x8) in a higher lane width slot (e.g., x16).