IBM X3950 X5 Problem Determination And Service Manual page 206

The following illustration shows the locations of the DIMM connectors on the
memory expansion module system-board tray.
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IBM System x3850 X5 and x3950 X5 Types 7145, 7146, 7143, and 7191: Problem Determination and Service Guide
- The following table lists the DIMM installation sequence for
memory-mirroring mode.
Table 24. Memory-mirroring mode DIMM population sequence for the memory expansion
module
Sets of 4 DIMMs
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Note: When you populate DIMMs in the memory expansion module,
populate the larger capacity DIMMs first, then the smaller capacity DIMMs.
DIMM connector population sequence
9, 16, 28, 29
1, 8, 20, 21
11, 14, 26, 31
3, 6, 18, 23
10, 15, 27, 30
2, 7, 19, 22
12, 13, 25, 32
4, 5, 17, 24