4GB RAM Memory Upgrade for HP Workstation Z400 PC3-10600E DDR3 1333MHz 2Rx8 ECC Unbuffered UB DIMM Module (PARTS-QUICK Brand) at Amazon.com
A-Tech 8GB Kit (2X 4GB) DDR3 1333MHz PC3-10600E 2Rx8 240-pin ECC-Unbuffered DIMM for HP Workstation Z200 and Z400 – Server Memory Ram Modules at Amazon.com
2X 4GB 2RX8 PC3-10600E 1.5V DDR3 1333MHz ECC Memory RAM Unbuffered for Server Workstation(4G) - Walmart.com