8GB DDR4 PC4-21300 2666MHz 288-pin DIMM. 16GB DDR4 PC4-21300 2666MHz 288-pin DIMM. 32GB DDR4 PC4-21300 2666MHz 288-pin DIMM. You can install different sized modules together in your machine. For example: Installing 2 x 8GB alongside 2 x 4GB will be 100% compatible.
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