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Hardware options installation 55
Qualified memory is performance-tuned for HP ProLiant and BladeSystem servers and provides future
enhanced support through HP Active Health and manageability software.
Certain performance features are unique with HP SmartMemory. HP SmartMemory 1.35V DDR3-1333
Registered memory is engineered to achieve the same performance level as 1.5V memory. For example,
while the industry supports DDR3-1333 RDIMM at 1.5V, the ML350e server supports DDR3-1333 RDIMM up
to 2 DIMMs per channel at 1333 MT/s running at 1.35V. This equates to up to 20% less power at the DIMM
level with no performance penalty. In addition, the industry supports UDIMM at 2 DIMMs per channel at
1066 MT/s. HP SmartMemory supports 2 DIMMs per channel at 1333 MT/s, or 25% greater bandwidth.
Memory subsystem architecture
The memory subsystem in this server is divided into channels. Each processor supports three channels, and
each channel supports two DIMM slots.
- Memory
subsystem
channel
(Processor 2)
Population
order
Slot number
(Processor
2)
- Memory
subsystem
channel
(Processor
1)
Population
order
Slot number
(Processor
1)
Processor 2
1
A
D
1
2
Processor 1
3
F
C
1
2
Processor 2
2
B
E
3
4
Processor 1
2
E
B
3
4
Processor 2
3
C
F
5
6
Processor 1
1
D
A
5
6
For the location of the slot numbers, see "DIMM slots ("General DIMM slot population guidelines" on page
57)."
This multi-channel architecture provides enhanced performance in Advanced ECC mode. This architecture
also enables Lockstep and Online Spare Memory modes.
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-rank, dual-rank, 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 server 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 8-GB single-rank DIMMs, a dual-rank DIMM would be 16
GB, and a quad-rank DIMM would be 32 GB.
LRDIMMs are labeled as quad-rank DIMMs; however, they function more like dual-rank DIMMs. There are
four ranks of DRAM on the DIMM, but the LRDIMM buffer creates an abstraction that allows the DIMM to