Upgrading an hp z400 (six slots) - HP Support Community - 7156445
CMS 8GB (2X4GB) DDR3 10600 1333MHZ ECC Non Registered DIMM Memory Ram Upgrade Compatible with HP/Compaq® Workstation Z400 Workstation for Server Only - B80
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)
HP Z400 48GB Memory/Ram Install - YouTube
16GB KIT (4 x 4GB) for HP-Compaq Z Workstation Series Z200 Z400 (4 DIMM Slots)
HP Workstation Z400 Memory Upgrades @Memory.NET
HP Z400 Workstation Xeon 3.3 GHz - HDD 500 GB RAM 8GB | Back Market
J9P81AA Certified Memory for HP Z400/Z440/Z600/Z640/Z800/Z840 4GB DDR4 ECC Reg. | eBay