HP ProLiant xw460c Blade Workstation - Manual (Page 29)

Hardware options installation 29
The memory subsystem for this server is divided into two branches. Each memory branch is essentially a
separate memory controller. The FBDIMMs map to the two branches as indicated in the following table:
Branch 0 Branch 1
FBDIMM 1A FBDIMM 5B
FBDIMM 3A FBDIMM 7B
FBDIMM 2C FBDIMM 6D
FBDIMM 4C FBDIMM 8D
This multi-branch architecture provides enhanced performance in Advanced ECC mode. The concept of
multiple branches is important for the operation of online spare mode and mirrored memory mode.
If the server contains more than 4 GB of memory, consult the operating system documentation about
accessing the full amount of installed memory.
Advanced ECC memory
Advanced ECC memory is the default memory protection mode for this server blade. In Advanced ECC,
the server blade is protected against correctable memory errors. The server blade provides notification if
the level of correctable errors exceeds a pre-defined threshold rate. The server blade does not fail
because of correctable memory errors. Advanced ECC provides additional protection over Standard ECC
because it is possible to correct certain memory errors that would otherwise be uncorrectable and result in
a server blade failure.
Whereas standard ECC can correct single-bit memory errors, Advanced ECC can correct single-bit
memory errors and multi-bit memory errors if all failed bits are on the same DRAM device on the
FBDIMM.
In addition to general configuration requirements, Advanced ECC memory also has the following
configuration requirements:
• FBDIMMs must be installed in pairs.
• FBDIMMs must be installed in sequential order, beginning with bank A.
In Advanced ECC mode, FBDIMMs must be populated as specified in the following table:
Configuration Bank A
1A and 3A
Bank B
5B and 7B Bank C
2C and 4C Bank D
6D and 8D
1 X — — —
2 X X — —
3 X X X —
4 X X X X
Online spare memory configuration
Online spare memory provides protection against degrading FBDIMMs by reducing the likelihood of
uncorrectable memory errors. This protection is available without any operating system support.
An understanding of single-rank and dual-rank FBDIMMs is required to understand memory usage in
online spare mode. FBDIMMs can either be single-rank or dual-rank. Certain FBDIMM configuration
requirements are based on these classifications. A dual-rank FBDIMM is similar to having two single-rank
FBDIMMs on the same module. Although only a single FBDIMM module, a dual-rank FBDIMM acts as two
separate FBDIMMs. The purpose of dual-rank FBDIMMs is to provide the largest capacity FBDIMM for the
current DRAM technology. If the current DRAM technology allows for 2-GB single-rank FBDIMMs, a dual-
rank FBDIMM using the same technology would be 4-GB.