Memory Subsystem Architecture; Single-, Dual-, And Quad-Rank Dimms - HP ProLiant SL250s Gen8 Server User Manual

while the industry supports DDR3-1333 RDIMM at 1.5V, this Gen8 server supports DDR3-1333 RDIMM at
1.35V. This difference equates to up to 20% less power at the DIMM level with no performance penalty.

Memory subsystem architecture

The memory subsystem in this node is divided into channels. Each processor supports four channels, and
each channel supports two DIMM slots, as shown in the following table.
Channel
1
2
3
4
For the location of the slot numbers, see "DIMM slot locations."
This multi-channel architecture provides enhanced performance in Advanced ECC mode. This architecture
also enables the Lockstep memory mode.
DIMM slots in this server are identified by number and by letter. Letters identify the population order. Slot
numbers indicate the DIMM slot ID for spare replacement.

Single-, dual-, and quad-rank DIMMs

To understand and configure memory protection modes properly, an understanding of single-, dual-, and
quad-rank DIMMs is helpful. Some DIMM configuration requirements are based on these classifications.
A single-rank DIMM has one set of memory chips that is accessed while writing to or reading from the
memory. A dual-rank DIMM is similar to having two single-rank DIMMs on the same module, with only one
rank accessible at a time. A quad-rank DIMM is, effectively, two dual-rank DIMMs on the same module. Only
one rank is accessible at a time. The node memory control subsystem selects the proper rank within the DIMM
when writing to or reading from the DIMM.
Dual- and quad-rank DIMMs provide the greatest capacity with the existing memory technology. For
example, if current DRAM technology supports 2-GB single-rank DIMMs, a dual-rank DIMM would be 4-GB,
and a quad-rank DIMM would be 8-GB.
Slot
A
E
B
F
C
G
D
H
Slot number
1
2
3
4
8
7
6
5
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