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Extensible Firmware Interface Specification
12-6 12/01/02 Version 1.10
Figure 12-5 shows an example of a server with one PCI Host Bus and two PCI Root Bridges. Each
of these PCI Root Bridges is a different PCI Segment which allows the system to have up to
512 PCI Buses. A single PCI Segment is limited to 256 PCI Buses. These two segments do not
share the same PCI Configuration Space, but they do share the same PCI I/O, PCI Memory, and
PCI Prefetchable Memory Space. This is why it can be described by a single PCI Host Bus. The
firmware for this platform would produce two instances of the PCI Root Bridge I/O Protocol.
OM13163
PCI Segment 0
Core Chipset Components
PCI Host Bus
PCI RB
PCI Segment 1
PCI RB
Figure 12-5. Server System with Two PCI Segments