IBM Power 720 Overview page 100

General rules for 12X IO Drawer configuration
If you have two processor cards, spread the I/O drawers across two busses for better
performance. Figure 2-27 shows configuration examples to attach 12X I/O Drawers to a
Power 720. Other options are also available.
Figure 2-27 12X I/O Drawer configuration for a Power 720 with one GX++ slot
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IBM Power 720 and 740 Technical Overview and Introduction
720
PCIe
One I/O-Drawer
720
PCI-X
One I/O-Drawer
720
PCIe
PCIe
Two I/O-Drawers
PCI-X
720
PCI-X
PCI-X
PCI-X
Four I/O-Drawers