Have installed 6 X 16gb hp ECC ram, win 10 says ram is 96gb but only 64gb useable, not sure why .

[Johno_6]

Running with 6 X 16 GB dimms but windows says only 64gb useable help!!!!

[DGroves]

the z600 (v2) like the z800 uses a triple channel memory controller as such ram banks are in groups of 3 not 2

for the later v2 motherboards with 6 dimm slots

the max ram per HP was 48GB for the z600

• Maximum

  24 GB ECC-UDIMM with 2 CPUs

  48 GB RDIMM with 2 CPUs

and the unofficial max ram capacity is 96GB (limitation of the memory controller in the CPU) for the v2

motherboard with 6 dimm slots using registered ECC type ram

this is a unsupported memory configuration that HP never certified and later "high density" 16gb modules may not work you might need the older low density dimms which have more memory chips on the dimm

https://cloudninjas.com/collections/hp-z600-c2-ram-memory-upgrade#:~:text=The%20HP%20Z600%20Workstat....

https://h20331.www2.hp.com/Hpsub/downloads/Mini-WP_Z600_memory.pdf