You can upgrade your HP Compaq Z400 Workstation (4 DIMM Slots) Computer to up to a maximum memory capacity of 16GB Memory. How many total memory slots to install memory? The Computer has 4 Slotsto install memory, already with 4GB standard memory installed. 4GB RAM Memory for HP-Compaq Z400 Workstation (6 DIMM Slots) (DDR3-10600 - ECC). HP Z400 Workstation KK719ET. The PCIe x8 connectors are open ended, allowing a PCIe x16 card to be seated in the slot. If your HPE Workstation Z400 (w/6 DIMM slots) memory upgrade fails at anytime–we will ship a replacement same day. We support your HPE Workstation Z400 (w/6 DIMM slots) memory purchase long after the sale. Meet the increasing demands of your applications with more HPE Workstation Z400 (w/6 DIMM slots) memory.