No, the ASRock Rack X470D4U does not support asynchronous dual channel memory.
No, the ASRock Rack X470D4U does not support asynchronous dual channel memory.
I'm choosing one of these boards to swap in for your NAS setup. This aims to boost stability and ensure better OS compatibility, along with server capabilities such as wake on LAN and IPMI support. Currently, I'm using 48 GB memory (two 16 GB and two 8 GB modules) in asynchronous dual-channel configuration. The manual mentions "dual channel technology" but doesn't specify asynchronous details. It states identical pairs of DIMMs are required, which might mean each channel needs matching or all four sticks must match. This could imply removing the 8 GB modules if they don't fit. It's not a major issue unless I have to replace them. Overall, more memory is better in this situation. The relevant part of the manual is on page 22 (page 28 in the PDF due to cover formatting) titled X470D4U.pdf.
I believed all DIMMs should match in each channel, not just for this specific board. Although it functions on certain boards, the guide indicates it won’t work there.
This technique has worked well for years to boost dual-channel performance. In the DDR2 time, using 2GB+1GB per channel gave you around 6GB; in DDR3, 4GB+2GB per channel yielded 12GB. I once ran an aunt's old Pentium 4 with 512MB+256MB DDR, which was impressive. Dual-channel speed drops when the system runs asynchronously, shifting to single-channel mode once memory usage hits about two-thirds of capacity—something that usually occurs after upgrading. Having equal memory per channel avoids this issue. However, pushing heavy overclocking or high XMP settings like DDR4-4000 can cause problems, especially with more than two sticks regardless of their size. I’ve generally had good memory compatibility, so these experiences might be exceptions.
Having the 16GB dimmer slots on the left and the 8GB on the right would likely keep you in hybrid dual-channel mode. I don’t think that’s the same as asynchronous. It seems like you’re still using dual-channel until the A and B channels don’t match, which means you need more memory. Edit: @YoungBlade provided clearer details. The optimal setup is 16|8|16|8 or 8|16|8|16, just running normally in dual-channel. Channel A and B should have identical settings. Some boards are quite sensitive to the dimmer positions in A1/B1 and A2/B2, but it usually doesn’t matter much.
It's surprising how mixing capacities in one channel works. I expected it to fail or just rely on the smaller module's capacity. I'm planning to test it after receiving the board.