IBM Power 780 Technical Overview And Introduction page 66

Table 2-4 shows the optimal placement of each DIMM-quad within a dual-enclosure system.
Each enclosure must have at least two DIMM-quads installed.
Table 2-4 Optimum DIMM-quad placement for a dual enclosure system
Memory controller
J1A J2A
Q1 Q1
Memory controller
J1A J2A
Q3 Q3
Quads Q1 and Q2 must be identical to each other. Quads Q3 and Q4 must be identical to each other.
Note: For maximum memory performance, the total memory capacity on each memory controller
must be equivalent.
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IBM Power 770 and 780 (9117-MMD, 9179-MHD) Technical Overview and Introduction
CPU 1 CPU 3
Memory controller
J3A J4A J5A J6A
Q2 Q2 Q1 Q1
CPU 1 CPU 3
Memory controller
J3A J4A J5A J6A
Q4 Q4 Q3 Q3
Enclosure 1
CPU 4
Memory controller
J7A J8A J1B J2B J3B
Q2 Q2 Q5 Q5 Q8
Enclosure 2
CPU 4
Memory controller
J7A J8A J1B J2B J3B
Q4 Q4 Q6 Q6 Q7
CPU 2
Memory controller
J4B J5B J6B J7B J8B
Q8 Q5 Q5 Q8 Q8
CPU 2
Memory controller
J4B J5B J6B J7B J8B
Q7 Q6 Q6 Q7 Q7