4GB 2 X 2GB PC2-5300F 667MHz 240 pin DDR2 SDRAM ECC Fully Buffered FB DIMM Server Low Power Memory for HP Workstation XW8600 (PARTS-QUICK BRAND). Equivalent to HP Part Numbers: 397413-B21, 442823-B21, 461828-B21, EM161AA (2pcs) Capacity: 4GB 2 X 2GB Kit FULLY BUFFERED DIMM FB LOW POWER MEMORY Form Factor: 240 pin DIMM Warranty: Lifetime ONLY FOR THE SERVER LISTED DO NOT BUY FOR STANDARD DESKTOPS WHICH USE NON-ECC MEMORY