The fact that CPUs based on Zen 4 and therefore socket AM5 do not support PCIe 5.0 took us by surprise, but there are reasons for AMD to boycott the fifth generation of the famous parallel interface.
The key is on the Infinity Fabric bus
Infinity Fabric is a concept that we have read over and over at AMD in recent years, it is a proprietary interconnect that AMD uses to communicate with each other the different elements of its APU / SoC, CPU and GPU
An important variant of the Infinity Fabric is its IFOP variant, which is an external interface that allows different chips to communicate with each other. With IFOP, it is possible to directly communicate a CPU and GPU without the need for PCI Express and since it is a proprietary interface from AMD, it allows them to sell their CPU and GPU together to computer manufacturers. gaming laptops. With this they manage to block access to Intel and NVIDIA GPUs, ensuring a purely AMD ecosystem.
To this we have to add that AMD recently licensed MediaTek WiFi radio so as not to depend on Intel radios for laptops with AMD CPU and GPUs.
Why doesn’t AMD want PCIe 5.0 in AM5?
One of the novelties that the fifth generation of PCI Express will bring is the addition of protocolo CXL, which enjoys great support from the industry and which, among others, adds a system of consistency with the memory addressing of the CPU. In other words, while AMD’s Infinity Fabric gives HyperTransport a system of consistency, CXL does it with PCIe.
We don’t know if Intel will use PCI Express with CXL in its GPUs with the DG2 architecture, but it is very possible that they will use this protocol. AMD’s decision is therefore clear, to avoid building gaming laptops that combine their processors with Intel GPUs.
Since the introduction of its AMD RX 6000 and its Smart Access Memory, a rebranding of the PCIe Resizable BAR, we know that AMD seeks to create a closed ecosystem in PC based solely on its products. Intel, on the other hand, is also looking to do the same and the two are said to seek to marginalize themselves together. AMD’s move is also aimed at preventing rival NVIDIA from launching graphics cards that are compatible with PCIe 5.0.