Hardware options installation 37
Single- and dual-rank DIMMs
DIMM configuration requirements are based on these classifications:
•
Single-rank DIMM
−One set of memory chips that is accessed while writing to or reading from the
memory.
•
Dual-rank DIMM
−Two single
-rank DIMMs on the same module, with only one rank 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-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.
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
12800 = 1600-MT/s
10600 = 1333-MT/s
8500 = 1066-MT/s
6
DIMM type
R = RDIMM (registered)
E = UDIMM (unbuffered with ECC)
L = LRDIMM (load reduced)
