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  9. 2.1.2 Number of CPUs and Number of Root Complexes

2.1.2 Number of CPUs and Number of Root Complexes


2.1.2 Number of CPUs and Number of Root Complexes
A root complex consists of an I/O controller mounted on a processor and the PCI switches, PCI devices, etc. under the I/O controller.
The number of root complexes varies depending on the CPU configuration. The maximum number of mounted PCI cards and the available PCI slots vary depending on the number of root complexes.
For cases of CPU module expansion after the installation of equipment to change to the 2-CPU configuration, if the I/O bus is not reconfigured, apply the rules for the 1-CPU configuration.
For details on root complexes, see "2.3 Relationship Between the CPU Configuration and Number of Root Complexes."
Note - For cases of CPU module expansion after the installation of equipment to change to the 2-CPU configuration, the recommended configuration is one with four root complexes. This configuration inherits the I/O bus configuration and mounting rules of the 1-CPU configuration. Changing the configuration into one with eight root complexes increases the maximum number of mounted PCI cards. However, system reconfiguration is required for reconfiguring the I/O bus.