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82 Installing System Components
General Memory Module Installation Guidelines
To ensure optimal performance of your system, observe the following guidelines when configuring your
system memory.
• Use only qualified FBDs. FBDs can be either s
ingle-ranked
or d
ual-ranked
. FBDs m
arked with a 1R
are single
-r
anked and modules marked with a 2R are dual
-r
anked.
• A minimum of two identical FBDs must installed.
• DIMM sockets must be populated by lowest number first.
• FBDs m
ust be installed in pairs of matched memory size, speed, and technology
, and the total
number of FBDs in the configuration must total two, four, or eight. For best system performance, all
FBDs should be identical memory size, speed, and technology.
•Memory sp
aring and
memory m
irroring require
e
ight FBDs, and all FBDs must be of identical
memory size, speed, and technology.
• Memory sparing and memory mirroring cannot be implemented at the same time.
Non-Optimal Memory Configurations
System performance can be affected if your memory configuration does not conform to the preceding
installation guidelines. Your system may issue a warning message during startup stating that your
memory configuration is non-optimal.
Memory Sparing Support
The system supports memory sparing if eight identical memory modules are installed in the system. The
memory sparing feature must be enabled in the System Setup program and can be used only if memory
mirroring is not enabled.
Memory sparing allocates four ranks of DIMM memory to the spare bank of memory sparing. These four
ranks consist of the first rank of memory in DIMM sockets 1 through 4. For single-rank DIMMs, the
entire capacity of the four DIMMs is allocated to sparing whereas for dual-rank DIMMs, only half of the
four-DIMM capacity is allocated to sparing. Table 3-7 shows how memory sparing splits the available and
spared memory in each of the single- and dual-ranked memory module combinations.
Table 3-7. Memory Sparing Configurations
DIMMs Size/Type Total Memory Available Spare
8 256-MB single-rank 2 GB 1 GB 1 GB
512-MB single-rank 4 GB 2 GB 2 GB
1-GB single-rank 8 GB 4 GB 4 GB
2-GB single-rank 16 GB 8 GB 8 GB
2-GB dual-rank 16 GB 12 GB 4 GB