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, and an octal-rank LRDIMM would be 64 GB.
LRDIMMs are labeled as quad- and octal-rank DIMMs. There are four and eight ranks of DRAM on the
DIMM, but the LRDIMM buffer creates an abstraction that allows the DIMM to appear as a logical dual-
rank DIMM to the system. This is called Rank Multiplication. The LRDIMM buffer also isolates the
electrical loading of the DRAM from the system to allow for faster operation. These two changes allow the
system to support up to two LRDIMMs per memory channel, providing for greater memory capacity and
higher memory operating speed compared to quad-rank RDIMMs.
DIMM label identification
To determine DIMM characteristics, see the label attached to the DIMM. The information in this section
helps you to use the label to locate specific information about the DIMM.
Item Description Definition
1 Capacity
8 GB
16 GB
32 GB
64 GB
128 GB
2 Rank
1R = Single rank
2R = Dual rank
4R = Quad rank
8R = Octal rank
3 Data width on DRAM
x4 = 4-bit
x8 = 8-bit
4 Memory generation
PC4 = DDR4
Table Continued
DIMM label identification 67
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