B650 vs B650E: Is PCIe 5.0 Support Really Differen

Hey folks,

I've been doing some research on the ASRock Steel Legend WiFi B650 and B650E motherboards, and I've noticed conflicting opinions about their PCIe 5.0 support.

Some people claim that while the B650 technically supports PCIe 5.0, its actual speeds are more like PCIe 4.0, whereas the B650E delivers true PCIe 5.0 performance. On the other hand, others say there?™s no difference and both can deliver full PCIe 5.0 speeds.

This has left me a bit confused.

Can anyone with direct experience or more knowledge clarify this? Is the B650 actually limited to PCIe 4.0 in most cases, or does it fully support PCIe 5.0 just like the B650E?

Thanks in advance for the insights!

Here reddit posts :
https://www.reddit.com/r/ASRock/s/NvQBgDoggp
https://www.reddit.com/r/ASRock/s/bHav0GOQjn

The PCIe lanes for the main PCIe slot (x16, usually used for a GPU), and the main m.2 slot (x4) have absolutely nothing to do with the chipset. They're directly connected to the AM5 socket (to/from the CPU).

The only two possible differentiating factors are 1) wire traces on the motherboard, and 2) software (firmware).

That's why they can make PCIe Gen.5 m.2 slot as *OPTIONAL* for B650.

Questions are, did the motherboard manufacturer design the traces to support Gen.5 speeds, or went for cost reduction instead? As for the main PCIe slot, same applies. Is the cost reduction worth the trouble of designing two different traces? The main cost reduction would come from manufacturing instead, since not supporting Gen.5 speed would require less layers, etc.

If not, then it's purely software limiting what will be enabled -> artificial market differentiation.

If the B650 motherboard is designed and advertised as supporting Gen.5 NVMe drive, then it should work as advertised and give you full Gen.5 speed, since that link is direct to the CPU. This only applies to the main m.2 NVMe slot!

No B650 motherboard should be advertised as supporting Gen.5 PCIe x16 slot, as that is against AMD's market differentiation tactics. Even if the CPU & the board are physically capable of supporting that, software (firmware) will prevent that from working.

Note some AM5 CPU's don't support Gen.5 at all, such as the 8000G-series APU's. These are based on either Phoenix of Hawk Point dies, and don't support PCIe Gen.5. It doesn't matter if you put them on an X870E motherboard. The CPU will be limited to Gen.4 speeds.


Edited by eccential - 02 Jan 2025 at 11:32pm

NDRE28 wrote: As you can see, B650 offers 4 CPU PCIe 5.0 lanes, while B650E offers 24 CPU PCIe 5.0 lanes. That's a huge difference!

Chipset offers no *CPU* PCIe lanes. Chipset merely offers its own PCIe lanes.
The main PCIe x16 slot, the main NVMe x4 slot, and 4 more lanes are connected directly to the AM5 socket. These PCIe lanes have absolutely nothing to do with the chipset.

The chipset merely disables PCIe Gen5 functionality that is already on the CPU. It is purely a market segmentation play. In fact, I bet B650E and B650 are the exact same silicons.

See 1-2 Motherboard Block Diagram (provided by Gigabyte) in the following page:
https://www.tomshardware.com/features/x670-motherboard-overview

That image is an X-series chipset example, so there are 2 chipsets. B-series is just single chipset, but the connection is basically the same. It's just not daisy chained.

AM5 socket provides 28 PCIe lanes.
Typical motherboard will route them:
16 to main PCIe slot
4 to main NVMe slot
4 to either a PCIe slot or to second NVMe slot
4 to the chipset

Connection to the chipset can be Gen5 (X-series) or Gen4 (B-series), and the chipset will provide additional PCIe slots and USB/SATA functions. All of these chipset-provided function will ultimately have to go through the 4 lanes to the CPU, so that will be the bottleneck. And this is why it's best to use the CPU-direct lanes for your most demanding hardware (GPU, main NVMe storage, etc.) if possible.