AMD’s masterful Zen 4 motherboard chipset strategy, what it enables and why it matters

amd ryzen 7000 series render

AMD’s X570 chipset was stacked with powerful I/O, but presented a significant annoyance for buyers: it required active cooling. This meant a throwback to the days when the use of ever faster memory meant that motherboard chipsets – where the memory controller resided – began to require heatsinks with fans.

Well, good news: AMD’s Socket AM5 chipsets don’t require a fan. This even includes the top-end X670E model as well as the standard mid-range X670 and B650 chipsets. What they will need is a significant amount of space on the motherboard, as well as a significant passive heatsink. This is because the two variants of the X670 chipset are actually a “chipset”, with two separate dice.
motherboard msi dual chipset am5

It’s actually been rumored for a while, but most people expected it to be two chips in one package, much like AMD’s Ryzen processors. Instead, as we can see in this screenshot from MSI’s “Inside Computex 2022” live stream (embedded below), there are clearly two separate chips on the board in their own packages.

In the stream, MSI’s Eric van Beurden and Michiel Berkhout reviewed AMD’s announcements from Computex, then gave an overview of the Socket AM5 cards that will be available from MSI at launch. As part of this discussion they clarify that the AM5 socket has 28 PCIe lanes routed to it, and normally they will be configured such that sixteen lanes go to a PCIe graphics slot, two M.2 sockets get four lanes each , then the last four lanes are for chipsets.

socket am5 total io platform

This raises questions that haven’t been answered, like exactly how this will all be wired up. If the matched chipsets are wired in parallel, i.e. each chip receives two lanes, latency will be equal on all chips, but bandwidth will be limited by the two-lane interface. (That said, PCIe 5.0 x2 is functionally equivalent to PCIe 4.0 x4, which X570 connects to.)

Alternatively, if they are daisy-chained to the CPU socket, this could have significant latency implications for the second chipset, although it would allow any device on either chipset to connect to the processor at a maximum rate of 16 GB/second.

Anyway, X670 and X670E use a pair of these chips, while B650 only gets one. This means that the B650 will only have half the available I/O compared to the X670, but half of what AMD promised is probably sufficient for most users. AMD’s slide says Socket AM5 can have up to 14 SuperSpeed ​​USB ports, and some of them are likely connected directly to the CPU socket, which means that instead of wasting 7, you won’t ‘probably only lose 5 or 6.

In the stream, MSI’s Berkhout and Van Beurden also pointed out that MSI isn’t planning any Mini-ITX cards for the Socket AM5 launch. Between the enlarged CPU socket, dual chipsets, and their need for large passive heatsinks to avoid a noisy fan, Berkhout says we’re unlikely to see many X670 or X670E boards on ITX. Instead, Mini-ITX Socket AM5 boards will likely stay with the single-chip B650.

As to why AMD would do something like that, well, that’s really, really smart. Using a single chip in their product stack greatly simplifies logistics and planning, and placing a pair of chips on high-end boards is a simple solution for expanding I/O. It’s easy to imagine an enterprising motherboard vendor like Biostar using a PCIe switch to hook up even more chipset dice for a specialized board with expanded I/O.

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