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Hardware options installation 44
• Successive cache lines are interleaved between the DIMMs and the Lockstep SMI channels of the two
memory controllers in the processor such that adjacent cache lines reside on different memory
controllers, SMIs, DIMMs, and DIMM ranks for better performance. To take advantage of this feature,
DIMMs should be populated evenly between all SMI channels. If an SMI channel pair has more DIMMs
than others, the extra memory on that SMI channel pair does not benefit from the interleaving
mechanism across memory controllers.
Hemisphere mode
The Intel® Xeon™ 7500-series processor architecture incorporates Hemisphere mode, a high-performance
interleaving technology. Hemisphere mode combines the tracking resources of both memory controllers
within each processor for a more aggressive cache line pipelining.
Hemisphere mode is the only supported configuration, and is enabled in RBSU when processors in the system
have identical DIMM population behind both of their memory controllers. That is to say, all populated
memory cartridges are populated the same way.
• Hemisphere mode should produce the best overall performance for a variety of applications.
• To enable each processor to enter Hemisphere mode, both memory cartridges must be installed and
populated with equal memory capacities based on the DIMM installation guidelines (on page 41).
• Greater performance is obtained when all cartridges are populated with either four or eight dual- or
quad-rank DIMMs.
• The server supports Mirrored Memory mode while Hemisphere mode is enabled.
Memory performance optimization
The server supports 128 DIMMS across eight Multi-core processors (64 DIMMs across four multi-core
processors, in each processor memory drawer). While there are many DIMM population configurations that
can support any total memory size, optimal performance is achieved when populated DIMMs can take
advantage of the Intel® Xeon™ 7500-series processor architecture.
To achieve the best performance for a given memory processor configuration, observe the following
guidelines: