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AMD says AM5 platforms can support CUDIMMs, but won't commit to a release date

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But not with current CPUs?

Generic AMD AM5 CPU and motherboard
(Image credit: Shutterstock)

Even though AMD's AM5 platform is designed to support all features of DDR5 memory modules, including CUDIMMs, the company's existing Ryzen 7000 cannot work with CUDIMMs at all, whereas Ryzen 8000, and Ryzen 9000-series CPUs do not fully support such modules. Nonetheless, AMD's AMD's AM5 infrastructure has everything to support clock unbuffered memory modules, according to Sourabh Dhir, product management lead for gaming and workstations, who spoke to Digital Trends.

As memory technology evolves, innovations include not only memory chips with a higher data transfer rate but also new DIMM technologies, such as CUDIMMs. In fact, JEDEC's standards presume that all memory modules featuring memory speeds of 6400 MT/s and higher are CUDIMMs (i.e., have a clock driver onboard to ensure cleaner signaling and stability at high transfer rates).

According to AMD, CUDIMM support does not require a platform overhaul: AM5 is already equipped with everything needed to support all kinds of DDR5 enhancements. However, it may take AMD another generation of CPUs to fully support CUDIMMs, as Sourabh Dhir did not explicitly say that AMD's existing or upcoming processors will officially support CUDIMMs at some point.

For now, Ryzen 7000-series processors are completely incompatible with CUDIMM memory modules: if installed, the system will fail to boot. By contrast, Ryzen 8000 and 9000 series CPUs can technically work with CUDIMMs, but only in a limited fallback configuration known as 'bypass mode', which ignores the clock driver chip on the module and, therefore, offers no advantage. This means that the system will start in DDR5-3200 mode and will require manual adjustment of the memory transfer rate, and therefore, there will be no performance guarantees.

It is noteworthy that MSI confirmed that AMD's Ryzen 8000 and 9000 series processors will support CUDIMM memory modules on X870 and X870E motherboards. MSI's overclocker Toppc explained that MSI's latest X870 mainboards feature enhanced signaling capabilities, which improve compatibility with high-frequency memory modules. While Ryzen 8000 and 9000 CPUs could operate with CUDIMMs, the full extent of supported memory speeds is still unannounced, and it is unclear whether AMD's implementation will match the performance levels seen on Intel's Arrow Lake-S, which already supports speeds of 9,200 MT/s and higher.

Achieving transfer rates around 10,000 MT/s still relies on heavily optimized setups with cherry-picked memory chips and increased voltages, which limits near-term mainstream use. CUDIMM modules are designed for officially rated speeds starting at 6,400 MT/s, but most high-end CUDIMM kits are intended for Intel's platform. 

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Anton Shilov
Anton Shilov
Contributing Writer

Anton Shilov is a contributing writer at Tom’s Hardware. Over the past couple of decades, he has covered everything from CPUs and GPUs to supercomputers and from modern process technologies and latest fab tools to high-tech industry trends.

9 Comments Comment from the forums
  • ezst036
    If this were Intel it would require a new socket after only two CPU revisions. Tick tock my friends!
    Reply
  • edzieba
    ezst036 said:
    If this were Intel it would require a new socket after only two CPU revisions. Tick tock my friends!
    In this case: if they were Intel they would already be supporting it.
    Reply
  • thestryker
    I don't think it should be of any surprise that it's memory controller and not platform that needs to support it. CUDIMMs are just UDIMMs with a CKD which means the CPU needs to be able to properly interface with the CKD and that's the only change.
    Reply
  • Notton
    The newly launched Epyc 4005 series supports UDIMM, so not all hope is lost.
    Reply
  • alceryes
    Notton said:
    The newly launched Epyc 4005 series supports UDIMM, so not all hope is lost.
    I don't think that means what you think it means.

    (UDIMM is the most common form of memory and is used by almost all modern CPUs)
    Reply
  • Mr Majestyk
    My guess, next gen X970 MB's for Zen 6 will support CUDIMMS, B950 won't.

    I'm leaning more and more to waiting out Zen 5 for Zen 6 if for nothing more than the 12 cores ccd's. A 10800X3D with 12 cores would be a beast for work and play.
    Reply
  • palladin9479
    Memory support has nothing to do with chipset anymore, it's now all 100% up to the memory controller on the CPU. As long as the memory controller can recognize the CKD then it'll end up being automatically configured, otherwise the memory controller ignores the CKD entirely and that's what bypass mode is. Worst case is the memory controller freaks out and just gives up the ghost.
    Reply
  • Lucky_SLS
    How is the performance scaling in zen 5 beyond 6400mhz?

    Intel Arrow lake needs all that memory speed cuz it has worse latency compared to zen 5.
    Reply
  • alceryes
    Lucky_SLS said:
    How is the performance scaling in zen 5 beyond 6400mhz?

    Intel Arrow lake needs all that memory speed cuz it has worse latency compared to zen 5.
    It depends on the application.
    Right around 6100MHz to 6400MHz (depending on CPU, MB, etc.) is where the memory controller will have to be dropped to 1:2 speed instead of 1:1. But, once you get the memory up to (and above) 7000MHz or so, some applications will run marginally faster. It's not a major increase in performance unless you're running specific memory-intensive benchmarks.

    Also, AMD has some baked in performance (lowered latencies) when running the the fabric/memory controller at 2:3 (2000MHz IF and 3000MHz controller/RAM), which is why AMD always suggests running the IMC and memory at 3000MHz (6000 DDR).
    Reply