PCI-E 3.0 x16 slots that connect to an AMD Ryzen 2200G CPU

[TheDarkKnight]

I just want to make sure I understand the relationship of the PCI-E 3.0 x16 slot, on an A320M-based motherboard, with regards to the CPU.

I'm going to post some facts as I know them. Please correct me if I'm wrong:
AMD 2200/2400G both have a total 16 PCI-E 3.0 lanes on each CPU.
Of those 16 PCI-E 3.0 lanes 8 are wholly dedicated to using a discrete graphics card. Or to be more specific, 8 PCI-E 3.0 lanes can be traced from the CPU to a physical PCI E 3.0 slot on a motherboard.

The Tricky Part where it gets somewhat confusing.
The motherboard manufacturer can make a decision here to either 1) map the 8 PCI-E 3.0 lanes coming from the CPU back to 16 PCI-E 3.0 lanes on the actual physical slot. But use PCI-E 2.0 protocols so that while 16 physical lanes are being used, they're operating at equivalent speed of 8 PCI-E 3.0 lanes...is that possible?

Or is it more likely that the physical motherboard slot (PCI-E 3.0 x16) is fully compliant, i.e., you "could" hook up 16 lanes but since the CPU only supports 8 lanes, were only going to put 8 lanes between the x16 slot and x8 CPU?

The reason I ask this question is because of how ASRock describes their PCI-E 3.0 slot on an A320M motherboard. As being PCI-E 3.0 x16 slot but operating in PCI-E 2.0 x16 mode.
"- 1 x PCI Express 3.0 x16 Slot (PCIE2: x16 mode)*"

The above description sounds to me like the physical slot is literally going to use 16 lanes in PCI-E 2.0 mode. If that is in fact true, does the transfer speed change when it hits the x8 lanes on the motherboard and go back at 3.0 speeds?

Or is the whole communication process between the CPU and the x16 motherboard slot negotiated from the very beginning to be the fastest speed of the slowest component?

 

[VirtualLarry]

The reason I ask this question is because of how ASRock describes their PCI-E 3.0 slot on an A320M motherboard. As being PCI-E 3.0 x16 slot but operating in PCI-E 2.0 x16 mode.
"- 1 x PCI Express 3.0 x16 Slot (PCIE2: x16 mode)*"

They are NOT saying it's PCI-E 2.0. They're saying "PCIE2" - the second PCI-E slot from the top.

 

[TheDarkKnight]

Ah, thank you for clearing that part up. So, if I could ask for just a bit more clarification...the PCI-E 3.0 slot is in fact x16 physical lanes on the motherboard? Or are they just saying x16 more tongue-in-cheek in reference to the size or length of the physical slot itself? In other words, it's a stock x16 slot connector they slapped on the motherboard but will still only ever use x8 lanes.

And if that's the case why not put a PCI-E 3.0 x8 slot on the motherboard that is half the length I want some consumer transparency here!

EDIT: I just Googled x8 slots. They do in fact have those sizes. Is there a stability benefit to using an x16 slot to hold an x8 graphics card? If there is a tangible benefit outside the bandwidth I guess I would like to hear that. If not, ASRock and everybody else should be putting x8 slots on motherboards that only use x8 lanes.

On one hand, I get it. Even when your a motherboard manufacturer your probably pulling parts out of a box and slapping them on a motherboard in the easiest way possible. So, I guess my question having said that is, if the CPU can only use 8 lanes then that means any graphics card you ever plug into the slot can really only ever use 8 lanes is that right or would an x16 graphics card communicating directly with a monitor not necessarily be bottlenecked by the x8 lanes path from the slot to the CPU?

I just have no idea of the ratio of communication between the CPU and graphics card versus the graphics card and monitor. What is the ratio of communication between the two?

EDIT #2: Ah, I see what's going on a bit now. The ASRock motherboard description on the A320M-HDV says the PCI-E 3.0 x16 slot operates in x16 mode on Ryzen CPUs. I think that was true before the release of the AMD 2200/2400G pair but not anymore. NewEgg needs to update their product descriptions more often.