Dimm Installation Sequence; Memory Mirroring - IBM System x3550 M3 Type 4254 Problem Determination And Service Manual

v Do not install one quad-rank RDIMM in one channel and three RDIMMs in
another channel.
v Do not install 1.5V DIMMs and 1.35V DIMMs in the same server.
The following illustration shows the location of the DIMM connectors on the system
board.

DIMM installation sequence

Depending on the server model, the server may come with a minimum of one 2 GB
or 4 GB DIMM installed in slot 3. When you install additional DIMMs, install them in
the order shown in the following table to optimize system performance. In
non-mirroring mode, all three channels on the memory interface for each
microprocessor can be populated in any order and have no matching requirements.
Table 14. Non-mirroring (normal) mode DIMM installation sequence
Installed microprocessor
Microprocessor socket 1
Microprocessor socket 2

Memory mirroring

Memory-mirroring mode replicates and stores data on two pairs of DIMMs within
two channels simultaneously. If a failure occurs, the memory controller switches
from the primary pair of memory DIMMs to the backup pair of DIMMs. To enable
memory mirroring through the Setup utility, select System Settings → Memory. For
more information, see "Using the Setup utility" on page 259. When you use the
memory mirroring feature, consider the following information:
DIMM connector population sequence
3, 6, 9, 2, 5, 8, 1, 4, 7
12, 15, 18, 11, 14, 17, 10, 13, 16
Chapter 5. Removing and replacing server components
197