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Appendix A Need More PCIe Slots?
Multiple PCIe Expansion System Configurations
The PCI Express Local Bus Specification defines the bus as
hierarchical, where logical PCI to PCI Bridges (PPBs) may be used to
add "levels" to the PCI bus hierarchy within a PCIe switch. Because
hierarchies are organized systems arranged into different levels, you
can take advantage of this automatic organizing and layering to expand
the number of available PCIe slots beyond the number available in your
computer’s motherboard.
You can easily add two or more Magma expansion systems to your
current system in either a "fan-out" or "daisy-chain" configuration. Each
of these configurations has advantages and uses. To determine which
type of configuration you wish to use, you should first understand a few
basic facts:
1. In a desktop computer, the BIOS enumerates automatically
behind logical PCI bridges. In the Magma configuration, the
BIOS looks beyond the Host card to find any PCIe cards
installed in the expansion chassis behind a PCIe switch. The
PCIe switch, in turn, emulates logical PRBs. The BIOS can
then configure the cards and allocate resources. Empty PCIe
slots are ignored during configuration.
In theory, your computer “should” be able to travel across up to
255 PCIe buses to identify and configure all installed PCIe
cards. The 255 PCI bus limit is actually a theoretical maximum.
The practical limit is somewhat lower and differs from one
system to another, but should still be a fairly large number.
In a desktop computer the bus numbers tend to be lower (0, 1,
2, etc.). Once the BIOS is finished configuring everything and
assigning resources, the Operating System starts loading and
activates the PCIe cards found.
When adding more Expansion Systems to an existing system,
be sure to connect and test them “one-at-a-time.” This will allow
you to quickly resolve any connectivity, or other, issues right at
the start. DO NOT INSTALL any 3
rd
Party PCIe cards into any
system until ALL attached systems are working correctly.