AMD EXPO 1.2 adds CUDIMM but current Ryzen CPUs still use bypass mode
AMD EXPO 1.2 is now appearing in AM5 beta BIOS releases, but the update does not mean current Ryzen CPUs suddenly gain full DDR5 CUDIMM support.
This follows our earlier coverage of ASUS adding EXPO 1.2 support to X870 beta BIOS builds and AMD’s updated EXPO 1.2 feature set. ASUS has since listed more beta BIOS files on the ROG forum, including X870 and B850 boards. The listed changes include EXPO 1.2 support and new tuning options for Crosshair boards.
X670/B650 support pending
ASUS has also been asked about EXPO 1.2 support for older AM5 motherboards. SAFEDISK, who handles ASUS ROG beta BIOS updates on the forum, said X670 and B650 boards need more time. This suggests EXPO 1.2 is not limited to 800-series boards, although older 600-series support may arrive later through separate BIOS builds.
Source: ASUS ROG Forums
ASUS and MSI confirm CUDIMM is in bypass mode
The important detail is still the memory controller. ASUS said AM5 does not support CUDIMM fully and will still operate in bypass mode. Zen 5 CPUs do not support CUDIMM on the AM5 platform. In practice, this means CUDIMM modules can boot, but the CKD chip is not used in the same way as on a platform with full CUDIMM support.
MSI engineer and overclocker Toppc the EXPO 1.2 CKD setting only defines whether CKD is enabled. If the CPU integrated memory controller does not support it, the platform cannot use full CUDIMM functionality. Current Ryzen CPUs can therefore run these modules only in compatibility mode, often closer to standard DDR5 behavior.
The 1.2 CKD setting only defines whether CKD is enabled. If the CPU IMC doesn’t support it, it still won’t be supported. Setting it to enabled won’t prevent support. You can refer to the hardware information; this is a secret the motherboard manufacturer didn’t disclose.
— Toppc, MSI
Source: MSI/Toppc
EXPO 1.2
The new EXPO update reportedly adds new memory profile fields, module geometry, Ultra Low Latency mode and partial CUDIMM/CSODIMM handling. However, full CUDIMM support is now expected with next-generation Ryzen CPUs based on Zen 6, not with Ryzen 7000, Ryzen 8000G or Ryzen 9000 processors already on the market.
Source: MSI Toppc , ASUS ROG , Wccftech
