HP ProLiant BL660c Gen8 Server Blade - Manual (Page 35)

Hardware options installation 35
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 blade 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 8-GB single-rank DIMMs, a dual-rank DIMM would be 16
GB, and a quad-rank DIMM would be 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 dual-rank DIMM to the system. The
LRDIMM buffer isolates the electrical loading of the DRAM from the system to allow for faster operation. This
allows higher memory operating speed compared to quad-rank RDIMMs.
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)
U = Ultra low voltage (1.25v)
Blank or omitted = Standard
5
Memory speed 14900 = 1866-MT/s
12800 = 1600-MT/s
10600 = 1333-MT/s
8500 = 1066-MT/s
6 DIMM type R = RDIMM (registered)