Along with rumours that AMD's Zen 4 will launch exclusively supporting DDR5, motherboard manufacturers have also said that AMD is moving over to a chiplet design for its next-gen motherboards chips. AMD famously moved over to a chiplet design with its Zen 2 architecture, where it placed 7nm CPU chiplets alongside a 14nm I/O hub die, but a dual-chiplet motherboard chipset is a different beast entirely.
AMD works with ASMedia to design its motherboard chipsets, and it appears that it will only be the top-end X670 chipset which will use the dual-chiplet design. Apparently, both chiplets are identical (according to Tom's Hardware), but by doubling them up the X670 can offer twice the throughput and connectivity of the single-chip designs used for the B650. The chiplet dies themselves will be produced using TSMC's 6nm production process.
The single-chip implementation provides eight lanes of PCIe 4.0 connectivity, four of which are for PCIe 4.0 storage, with the rest split between SATA drives and USB ports. The X670 will presumably double this up to 16 lanes, massively bolstering the connectivity of the platform, and making it the platform of choice for fans of serious storage.
As already mentioned the AM5 platform will support DDR5 memory and also ushers in support for PCIe 5.0 for AMD, something that Intel's Alder Lake already supports. The next question is when we'll see PCIe 5.0 graphics cards, and it could well be AMD that's first to that particular party, as rumours are Nvidia is sticking with PCIe 4.0 for its next-gen "Ada" graphics cards.
Zen 4 and the accompanying shift to AM5 are due to launch later this year.