64GB Total memory using 4pc of 16GB DDR4, 2666MHz, Non-ECC, CL19, 2R, X8, 1.2V, Unbuffered, DIMM, 288-pin Max Capacity: 128GB Sockets: 4 Mixing modules or kits of different speeds/timings/voltages is not recommended and may cause instability If a K4 “Kit of 4” part is not listed for a particular speed/capacity, it is not recommended to install two K2 “Kit of 2” parts together. K4 kits are only listed if the configuration has been tested as stable. C Compatible with: Lifetime exchange or repair warranty against manufacturing defects by Computer Memory Solutions. Manufactured by Computer Memory Solutions. We don't use OEM or Generic Modules to avoid incompatibility. In most cases, you can mix manufacturer parts, however, all memory in the system will run at the slowest performance of the installed modules or CPU/processor capability. To maximize performance, we recommend that you install your memory modules in matched pairs. A 64-bit Operating System is required to utilize more than 4GB of memory.