Hardware options installation 46
NOTE: There may be more than one memory bus speed menu option.
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 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 2-GB single-rank DIMMs, a dual-rank DIMM would be 4-
GB, and a quad-rank DIMM would be 8-GB.
DIMM identification
To determine DIMM characteristics, use the label attached to the DIMM and the following illustration and
table.
Item Description Definition
1 Size —
2 Rank 1R = Single-rank
2R = Dual-rank
4R = Quad-rank
3 Data width x4 = 4-bit
x8 = 8-bit
4 Voltage rating L = Low voltage (1.35v)
Blank or omitted = Standard
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