I'm upgrading from an i7-13700K system to a Ryzen 9 9950X3D with an X870E motherboard for After Effects. I need as much memory capacity as possible, so using four modules is much more practical than buying a 128GB 2-stick kit. My current memory is three 32GB DDR5-5200 sticks and one 16GB DDR5-5200 stick. The mixed setup worked without trouble in my Intel system, but I've now tried multiple AM5 motherboards and two CPUs and still can't get consistent POST behavior.
I'm currently using an MSI Tomahawk X870E with the latest BIOS. The board often gets stuck on memory training at code 15, sometimes for half an hour, and even a pair of matching modules in the recommended slots has failed to boot consistently. One successful boot is often followed by another reboot that hangs indefinitely. I'd be happy with lower memory speeds if that's what it takes—capacity matters more to me than 5200 MT/s. What settings, memory configuration, or troubleshooting steps have worked for other people using four DDR5 modules on AM5?
4 Answers
The mixed capacity setup is probably the biggest obstacle. Three 32GB modules and one 16GB module are not a matched kit, and AM5 is particularly sensitive to uneven DIMM layouts. Intel platforms often tolerate these combinations better. If the three matching sticks do not remain stable by themselves, adding the fourth is unlikely to help. Realistically, you may need to run the modules around DDR5-3600 or replace them with a properly matched four-module kit; there may not be a setting that makes this particular combination reliable at 5200.
Four DDR5 sticks are much harder on the Ryzen memory controller than two, and the official support level for this CPU is only around DDR5-3600 with four modules. The advertised 5200–5600 speeds generally assume two matched sticks. Start with EXPO disabled and manually set the memory to 3600 MT/s. If that works, increase it gradually—3700, 3800, and so on—until you find the stable limit. A matched four-stick kit is also much more likely to work than three identical modules plus a different-capacity fourth stick.
I’d gladly run 112GB at a much lower speed if it stayed reliable. The problem is that even two matching sticks have occasionally failed to POST, so I’m trying to separate a basic platform problem from the limitations of the four-DIMM configuration.
Disable EXPO initially and also try disabling Memory Context Restore. That setting can make subsequent boots unreliable even when the initial training succeeds; disabling it makes booting slower but forces a more complete memory retraining. Once the machine is stable at conservative settings, you can experiment with frequency, timings, and the other memory-controller parameters.
Before tuning four modules, get the system stable with one stick and then two matching sticks in A2 and B2. Update the BIOS through the board’s flashback feature if possible, clear CMOS between major configuration changes, and check the CPU socket carefully for bent contacts. Memory training can take a while on the first boot, but repeatedly getting code 15 or a 0d error after a successful boot points to an unstable configuration or a hardware issue rather than simply needing more patience.
That matches what I’m seeing. The three matching modules once booted, but the next restart failed with a 0d error, and changing the installed DIMM combination became the only way to get another successful boot.