CMS 8GB (2X4GB) DDR3 10600 1333MHZ ECC Non Registered DIMM Memory Ram Upgrade Compatible with HP/Compaq® Workstation Z400 Workstation for Server Only - B80 at Amazon.com
CMS 12GB (3X4GB) DDR3 10600 1333MHZ ECC Non Registered DIMM Memory Ram Upgrade Compatible with HP/Compaq® Workstation Z200, Z210, Z400, Z600, Z800 for Server Only - B81 at Amazon.com
A-Tech 24GB ECC Unbuffered Memory Kit (6 x 4GB) for HP Z400 Workstation - ECC UDIMM DDR3 PC3-10600 1333MHz 240-Pin DIMM 2Rx8 1.5V Dual Rank RAM (AM080899) at Amazon.com