4GB Memory for HP Workstation xw4600 DDR2 PC2-6400 ECC UDIMM (PARTS-QUICK BRAND) Capacity: 4GB DDR2 800MHz ECC Unbuffered DIMM Form Factor: 240 pin DIMM Warranty: Lifetime ONLY FOR THE SERVER LISTED DO NOT BUY FOR STANDARD DESKTOPS WHICH USE NON-ECC MEMORY