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Hardware options installation 41
Memory subsystem architecture
The memory subsystem in this server is divided into channels. Each processor supports three channels,
and each channel supports three DIMM slots, as shown in the following table.
Channel Slot Slot number
1 G
D
A
1
2
3
2 H
E
B
4
5
6
3 I
F
C
7
8
9
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.
Memory configurations
To optimize server availability, the server supports the following AMP modes:
• Advanced ECC—provides the greatest memory capacity for a given DIMM size, while providing up
to 4-bit error correction. This mode is the default option for this server.
• Mirrored Memory—provides maximum protection against failed DIMMs. Uncorrectable errors in one
channel are corrected by the mirror channel.
• Lockstep—provides enhanced protection while making all installed memory available to the
operating system. The server can continue to function if a single- or mulit-bit memory failure within a
single DRAM device occurs.