6.4.3.3 DIMM Ranks
To understand and configure memory protection modes properly, it is helpful to learn about
single-rank, dual-rank, and quad-rank DIMMs. Some DIMM configuration requirements are
based on these classifications.
l A single-rank DIMM has one set of memory chips that are accessed while data is written
to or read from the memory.
l A dual-rank DIMM is, effectively, two single-rank DIMMs on the same module, with
only one rank accessible at a time.
l A quad-rank DIMM is, effectively, two dual-rank DIMMs on the same module, with
only one rank accessible at a time.
The server memory control subsystem selects a 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 the current DRAM technology supports 8 GB single-rank
DIMMs, a dual-rank DIMM can offer a capacity of 16 GB and a quad-rank DIMM can offer a
capacity of 32 GB.
LRDIMMs are labeled as quad-rank DIMMs. There are four 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. The LRDIMM buffer also isolates the electrical loading of
the DRAM from the system to allow for faster operation. These two changes provide a higher
memory operating speed compared with quad-rank RDIMMs.
6.4.3.4 DIMM Identification
To determine DIMM characteristics, see the label attached to the DIMM and refer to the
following figure and table.
Figure 6-31 DIMM identification
FusionServer G5500 Server
User Guide
6 Optional Part Installation
Issue 02 (2017-12-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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