AMD's 4th generation Ryzen "Renoir" desktop APUs, based on the "Zen 2" microarchitecture, could lack PCI-Express gen 4.0, hints the product page of an upcoming AMD B550 chipset motherboard by BIOSTAR. AMD already declared that the B550 lacks support for "Picasso," which means the "Ryzen with Radeon Vega Graphics" processors referenced in the BIOSTAR product page have to be "Renoir." On the mobile platform, Ryzen 4000H and 4000U series processors do lack PCIe gen 4.0, but it was expected that AMD will enable gen 4.0 for the desktop socket AM4 platform.

The lack of gen 4.0 support has implications for "Renoir." For starters, the APU, like its predecessors, spares only 8 PCIe lanes toward PEG (PCI-Express discrete graphics, or the main x16 slot you typically use for graphics cards). If these lanes are gen 3.0, then even the newer graphics cards, such as AMD's "Navi" RX 5700 XT, or next-gen GeForce "Ampere," would have to make do with a PCI-Express 3.0 x8 interface, despite being gen 4.0 x16-capable. We will test just how much of a bottleneck this poses, when the next-gen graphics cards come out.