64.0GB OWC Memory Upgrade Kit
4 x 16GB PC21300 2666MHz DDR4 RDIMM for Mac Pro (2019) 8-Core models
Product Specs:
IMPORTANT NOTES:
Mac Pro can use either RDIMM or LRDIMM, but they cannot be combined.
Mac Pro supports up to 12 DIMMs installed in configurations of 4, 6, 8, or 12 DIMMs. Configurations of 5, 7, 9, 10, and 11 DIMMs are not supported. Other configurations of 1, 2, and 3 DIMMs are for diagnostic use only.