OWC 32GB DDR4 2666MHz PC4-21300 CL19 1.2V 288pin Server DIMM ECC Registered memory compatible with Lenovo ThinkAgile (Xeon SP Gen 1) models HX3521-G, HX3720, HX3721, HX5520 and HX5521. 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 memory. 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 Lenovo part numbers 4X70P98203 and 7X77A01304.