What is PCI Express? Do PCIe lanes, slots, and versions matter?

What is PCI Express? Do PCIe lanes, slots, and versions matter? pci 4 in pci 3 slot PCIe Gen 3 x 1 PCI Slot x 3 30423052 B-Key x 1 (PCIe pcie gen 4 in gen 3 slot Can a PCI-E card work in a PCIPCI-X slot? The answer is no PCIe card and PCIPCI-X cards are not compatible with each other due to their

pcie gen 4 in gen 3 slot It should be backward compatible, but you will see less performance than if you had it in a PCIe slot since it runs at PCIe x8 instead

pcie 1x slot List of Motherboards with 3 PCI-Express x16 Slots: GIGABYTE B650 Gaming X AX V2, MSI X670E Gaming Plus WiFi, ASUS ROG Strix Z790-E Gaming WiFi II, 3 Slot x16 Gen4 PCI Express Backplane · One PCIe x16 Gen4 uplink slot · Two PCIe x8 Gen4 Add-On slots · PCIe Gen1, Gen2, Gen3 and Gen4 compliant