AMD's Ryzen 4000H APUs limited to only 8 PCIe 3.0 lanes for dGPUs? A non-issue mostly, even for dGPUs above an RTX 2060
The latest architectural analysis for the AMD’s Ryzen 4000H APUs made by IgorsLab reveals some more limitations imposed on the Renoir chips. We have seen how AMD is limiting DDR clocks for certain scenarios, and now it looks like dGPUs coupled with the Ryzen 4000H APUs may be restricted to only 8 PCIe 3.0 lanes instead of the full 16 lanes, but the downsides are negligible.
IgorsLab points out that lane restriction could lead to measurable bandwidth limitations in 1080p games running on dGPUs superior to the RTX 2060. This could explain why laptop OEMs do not bother to provide dGPU options above the RTX 2060. However, the estimated performance loss would be between 3% to 5% for an RTX 2070 running on only 8 PCIe 3.0 lanes, plus we must also not forget that Nvidia’s laptop dGPUs already have lower TGP specs. These limitations are most likely design choices meant to deal with power efficiency issues and to keep overall system costs as low as possible. AMD’s current goal is to offer competitive performance for ~US$1,000 gaming laptops, and the inclusion of more powerful dGPUs would clearly break that price barrier at this point in time. Moreover, laptops in this price category usually come with 1080p screens, so there is no real performance benefit with the inclusion of any dGPU above an RTX 2060.
Interestingly enough, the PCIe lane limit is not featured with the freshly-launched Ryzen 4000G desktop APUs. This was confirmed by AMD Director of Technical Marketing Richard Hallock, who specified in a recent Discord comment that the desktop APUs can access 24 PCIe lanes, of which 16 are allocated for the dGPU. It actually makes sense to raise the limit for desktop users, since system power limits are not really that big of a concern anymore.