What is PCIe x4 Slot

Our XMC-to-PCI Express Adapter 4X permits the use of a single-wide XMC module in a 4X PCIe slot PCI express lanes on the P15 XMC connector are

I explain in this video what is PCIe x4 on the motherboard and its uses I also explain what PCIe

4x4bet slot PCIe x4 is mostly for server grade network cards

4x4 joker slot In ASUS 「PCIe x16 Slots - 4」 - Motherboards Components , you could find most 4 x 5 x SlimSAS SATA 6Gbs 1-4