The MR9A Pro supports DDR4 ECC REG memory (common with Xeons) and non-ECC Nanya/Samsung consumer chips.
For enthusiasts, the "top" experience with this board usually involves flashing a modded BIOS to bypass factory limitations: [Request] Machinist X99 E5-MR9A PRO V1.1 BIOS Dump machinist x99 mr9a pro bios top
There is on this motherboard's BIOS. For a technical write-up, you would need to: The MR9A Pro supports DDR4 ECC REG memory