184 Upgrade and Maintenance Manual CX2550/60/70 M4
7.1 Basic information
– Each CPU offers 8 slots for DDR4 memory modules.
– Supported memory modules:
RDIMM with ECC, LRDIMM, 3DS-LRDIMM and AEP (Apache Pass) DIMM
–  Mixing of LRDIMM with RDIMM is not allowed.
– Unbuffered DIMMs are not supported.
– x4 and x8 DIMMs mixing is not allowed.
– Mixing of non-3DS and 3DS LRDIMMs is not allowed in the same channel, 
across different channels, and across different CPU sockets.
– Mixing of AEP DIMMs with RDIMMs is supported.
– Mixing of AEP DIMMs with LRDIMMs is supported.
– If DIMMs with different frequencies are mixed in the same channel, all 
DIMMs will run at the common lowest frequency.
– Mixing of DDR4 or AEP operating frequencies is not validated within a 
socket or across sockets by Intel CPU.
– There should be at least one DDR4 DIMM per CPU socket (slot 1A/1G).
– If only one DIMM is populated in a channel, then populate it in the slot 
furthest away from CPU.
– When single, dual and quad rank DIMMs are populated for 2DPC, always 
populate the higher number rank DIMM first (starting from the farthest slot), 
for example, first quad rank, then dual rank, and last single rank DIMM.
Figure 81: Mixing of DIMM types within a channel
DIMM types  RDIMM  3DS RDIMM  LRDIMM  3DS LRDIMM  AEP 
RDIMM 
allowed  not allowed  not allowed  not allowed  allowed 
3DS RDIMMs 
not allowed  allowed  not allowed  not allowed  allowed 
LRDIMM 
not allowed  not allowed  allowed  not allowed  allowed 
3DS LRDIMM 
not allowed  not allowed  not allowed  allowed  allowed 
AEP 
allowed  allowed  allowed  allowed  not allowed