Can someone clarify PCIe terminology of the B450 TOMAHAWK

MSI B450 TOMAHAWK MAX II b450 tomahawk max m 2 slot MSI B450 Tomahawk Max II Motherboard · Supports 1st, 2nd and 3rd Gen AMD Ryzen Ryzen with Radeon Vega Graphics and 2nd Gen AMD Ryzen with Radeon Graphics slot kronos Faetures: ; Multi-GPU, Supports 2-Way AMD® CrossFire™ Technology ; Storage, AMD® CPU 2 x SATA 6Gbs ports · 1 x slot

u1 slot machine B450 TOMAHAWK MAX ; Memory Channel Dual ; DIMM Slots 4 ; Max Memory 128 ; PCI-E x16 2 ; PCI-E Gen Gen3, Gen2