HPZ4 G4 Memory Not Recognized

[CompSMART]

Good day to all.

I recently picked up a used (off-lease) Z4 G4 workstation (Xeon W-2123 CPU) to replace my old Z400. When my Z4 arrived, it had 32GB ram with the following configuration:

(2) 8GB HP PN 864706-591 (installed in slots marked DIMM1 and DIMM8)

(2) 8GB SK Hynix PN HMA81GR7CjR8N-VK (installed in slots marked DIMM2 and DIMM7)

All was fine and no issue whatsoever during setup and config of the the workstation.  After I settled into my new workstation/configuration, I decided to add some RAM and ordered (4) Samsung M393A1K43BB1-CTD6Q (which is the same PN as is on the DIMMS with the HP label). 

I plugged the Samsung memory into the remaining slots (now fully populated with 8GB modules) and for some reason - the workstation only recognized 48GB of memory. I initially suspected 2 of the new Samsung dimms were bad so started from scratch adding only (2) dimms at time and making note of the memory change reported by the BOIS at boot. After a long period of playing musical dimms, I determined that for some reason the workstation appears not to recognize the memory plugged into the DIMM3 and DIMM6 slots. BUT - I need DIMMS plugged into the DIMM3 and DIMM6 slots in order for the workstation to recognize the dimms plugged into the DIMM4 and DIMM5 slots. SO... with all slots populated with 8GB dimms, the workstation only recognizes 48GB of memory. 

A system board test and memory test initiated from within the BIOS pass with no issues. Am I overlooking something here? or just dealing with some strange incompatibility between the different dimm brands?

Appreciate any advice/help - thank you!

[DGroves]

dimms must match not only in size but also speed,  rank, error correction or not,  buffered or not,  voltage 1.5 or 1.3  

you also need to match dimms within each memory channel, and some systems require largest dimm in first bank and others don't care, in dual cpu systems both cpu's need the same memory configurations

if you only have one cpu installed in a dual cpu system

then only the memory slots that have the single cpu installed will work

as you can see adding memory can be a challenge for some people

for your z4 g4 system,  these platforms have 4 channels, so install memory in sets of 4

look at these links, and pause it on the dimm install pictures

https://h20195.www2.hp.com/v2/getpdf.aspx/4AA7-2219ENW.pdf

https://www.youtube.com/watch?v=pbBlkwewmT0

[SDH]

Agree, again, with DGroves. Sounds like you have a hodgepodge of memory there. Some you state have the official HP-label attached. Some you say are the same as ones with the official HP-label attached (but maybe not given you suggest by lapse that those don't have the HP-label attached). Some are Samsung. Some are SKHynix. Some are what?

And, are you aware that HP bins its memory to higher than required source specifications? Thus, a stick with a HP official label on it may pass certain tests that other sticks without that HP-label may not.

Generally, if you get all HP-label sticks with the same HP Assembly P/N on the label you're safe to mix and match. However, I have found the very best results if I stick with HP-label sticks with same HP AS P/N number and same OEM brand. There are some alphanumerics at the end of the OEM's part number on their label that don't count (related to site of manufacture) but the HP-label with the correct HP AS P/N is the seal of quality and interchangeability.

This is why I prefer to get all used memory from eBay that has HP-labels with same HP AS P/N, and from same OEM vendor. Not to say I have not done well without following that rule... but you're not doing well. You should be seeing all memory sticks in your total, and are likely missing out on Quad Channel memory performance because you don't.

[CompSMART]

I appreciate all the replies and suggestions to my original post. Despite being branded differently, 6 of the 8 DIMMS all have the exact same Samsung label on them. Is it possible that HP or Lenovo (or whomever) brands the Samsung DIMMS has varying degrees of quality control? Yes. Is it probable to be the cause of my issue? I think not. Even taking into account the 2 non-Samsung DIMMS, they are of the same spec as the Samsung DIMMS (DDR3-2666, ECC, 1.2V, PC4-21300V-R) and function fine alongside the Samsung DIMMS (as long as they are not plugged into DIMM slots 3/4). Having spent more time researching on the internet, it appears that complaints about memory not being recognized in DIMM slots 3 and 4 are not uncommon and troubleshooting of them always seems to circle back to a bent CPU pin(s) or system board issues.

I'll post an update here when I identify and resolve the issue. 

[CompSMART]

Just to update everyone who replied to my message. After eliminating the DIMMS and system board as being possible causes of my issue, I began to suspect the memory controller in the CPU. After swapping out the CPU - upon first boot - all 8 DIMMS (64GB) were recognized.