Hardware options installation 24
Memory options (ML150 G6 servers)
IMPORTANT: This server does not support mixing RDIMMs and UDIMMs. Attempting to mix
these two types causes the server to halt during BIOS initialization.
The memory subsystem in this server can support RDIMMs or UDIMMs. Both types are referred to as
DIMMs when the information applies to both types. When specified as RDIMM or UDIMM, the
information applies to that type only. All memory installed in the server must be the same type.
The server supports the following DIMM speeds:
• Single- and dual-rank PC3-10600 (DDR-1333) DIMMs operating at 1333 and 1066 MHz
• Quad-rank PC3-8500 (DDR-1067) DIMMs operating at 1066 MHz
Depending on the processor model, the number of DIMMs installed, and whether UDIMMs or RDIMMs
are installed, the memory clock speed may be reduced to 1066 or 800 MHz. For more information on
the effect of DIMM slot population, see "General DIMM slot population guidelines (on page 26)."
Memory subsystem architecture
The memory subsystem in this server is divided into channels. Each processor supports three channels,
and each channel supports two DIMM slots, as shown in the following table.
Channel Slot Slot number
1 D
A
1
2
2 E
B
3
4
3 F
C
5
6
This multi-channel architecture provides enhanced performance in Advanced ECC mode. This architecture
also enables the Mirrored Memory and Lockstep memory modes. This server supports both Registered
PC3 DIMMs (RDIMMs) and Unbuffered DIMMs (UDIMMs).
DIMM slots in this server are identified by number and by letter. Letters identify the slots to populate for
specific AMP modes. Slot numbers are reported by ROM messages during boot and for error reporting.
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.
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