IBM System x3850 X5 Implementation Manual page 52

Figure 2-10 shows the x3850 X5 with the MAX5 attached.
Figure 2-10 IBM System x3850 X5 with MAX5 (the MAX5 is the 1U unit beneath the main system)
Figure 2-11 shows the MAX5 removed from the housing.
Figure 2-11 IBM MAX5 for the x3850 X5 and x3690 X5
MAX5 connects to these systems through QPI links and provides the EXA scalability
interfaces. The eX5 chip set, which is described in 2.1, "eX5 chip set" on page 16, is
contained in the MAX5 units.
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IBM eX5 Implementation Guide