ASROCK B450M Steel Legend PCIE Expansion Slot Question

[Buftor]

I have a question about this board. The CPU is Ryzen 5 3600. The board has two 16 lanes expansion slots. With this CPU, the specs are as follows:

1 x PCI Express 3.0 x16 Slot (PCIE2: x16 mode)
1 x PCI Express 2.0 x16 Slot (PCIE3: x4 mode)

I don't understand why even though the second slot is a 16 lane slot, it says in parentheses that it works in x4 mode?
Sorry for the newbie question, and thanks for any help.

 

[ShurikN]

It works in x4 mode because the CPU has only 24 pcie lanes to give.
4 are conected to the chipset, 16 to the main pcie slot (for a gpu) and the rest are technically multi-purpose lanes but usually used for nvme.
While the second slot is x16 in physical lenght, it's wiring is not, hence x4. It's also not connected directly to the cpu but the chipset instead.
I don't think B450 supports bifurcation anyway (spliting 16 cpu lanes into 2 x8 lanes for dual gpu setups)

 

[Buftor]

It works in x4 mode because the CPU has only 24 pcie lanes to give.
4 are conected to the chipset, 16 to the main pcie slot (for a gpu) and the rest are technically multi-purpose lanes but usually used for nvme.
While the second slot is x16 in physical lenght, it's wiring is not, hence x4. It's also not connected directly to the cpu but the chipset instead.
I don't thing B450 supports bifurcation anyway (spliting 16 cpu lanes into 2 x8 lanes for dual gpu setups)

Thanks, I understand now.