ECC REGISTERED UPGRADE: This type of memory is used in Workstations and Servers. It will NOT be compatible with standard desktop computers. Also, it cannot be mixed with UNBUFFERED -or- ECC LOAD REDUCED memory. OWC 64GB UPGRADE: Consists of a single 64GB DDR4 2666 PC4-21300 CL19 4Rx4 288-pin 1.2V ECC Registered DIMM Memory RAM Module Upgrade compatible with Fujitsu PRIMERGY model RX4770 M4. INDUSTRY LEADING: Consumer-friendly Advanced Replacement Program and Limited Lifetime Warranty, which includes Free Tech Support by Other World Computing. MAXIMIZE YOUR SERVER: With OWC's ECC Registered Server Memory, you will extend the life of your old infrastructure or save money when building a new one. Replacement for Fujitsu part numbers S26361F4026L764, S26361-F4026-L364, S26361F4026E764, S26361-F4026-E364 and S26361F4026E364.