DDR5 DIMMs installation order
This section contains information of how to install DDR5 DIMMs properly.
RDIMMs and 3DS RDIMMs installation order
For RDIMMs, 10x4 RDIMMs and 3DS RDIMMs, the following two memory modes are available. For 9x4
RDIMMs, only independent mode is available.
Independent mode installation order
In independent mode, memory channels can be populated with DIMMs in any order and you can populate all
channels for each processor in any order with no matching requirements. Independent mode provides the
highest level of memory performance, but lacks failover protection. The DIMM installation order for
independent mode varies based on the number of processors and memory modules installed in the server.
Independent mode installation rules
Follow the rules below when installing memory modules in independent mode:
• There should be at least one DDR5 DIMM per processor.
• All DDR5 memory modules must operate at the same speed in the same system.
• Memory population must be identical between processors.
• Memory modules from different vendors are supported.
• In each memory channel, populate the slot farthest from the processor (slot 0) first.
• All DIMMs must be all DDR5 DIMMs.
• x8 DIMMs and x4 DIMMs cannot be mixed in a system.
• All memory modules to be installed must be of the same type.
– 9x4 RDIMM cannot be mixed with non-9x4 RDIMMs in a system.
– 3DS RDIMM cannot be mixed with non-3DS RDIMMs in a system.
• All memory modules in a system must have the same number of ranks, except for below conditions:
– Single-rank RDIMMs can be mixed with dual-rank RDIMMs when there are 16 DIMMs populated for
each processor.
– Quad-rank 3DS RDIMMs can be mixed with octal-rank 3DS RDIMMs when there are 16 DIMMs
populated for each processor.
Note: System hang on POST may occur on a server operating in this configuration. In this case,
contact Lenovo service to replace the failed DIMM for proper operation.
– See
“Independent mode with mixing rank” on page 60 for more information on the installation
sequence when installing memory modules with different ranks.
The following table shows the sequence of populating memory modules for independent mode when only
one processor (processor 1) is installed.
Table 28. Independent mode with one processor
Total
DIMMs
Processor 1
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
1 DIMM
7
2 DIMMs
1
14 7
4 DIMMs
1
14 10 7 3
6 DIMMs
1
14 12 10 7 3 1
58 ThinkSystem SR630 V3 User Guide
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