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36 Appendix B Need More Slots?
2. The 4 and 7 Slot Magma Expansion Systems each add two (2)
PCI to PCI Bridges to the PCI Local Bus. The 13 Slot adds
three (3) PCI to PCI Bridges to the PCI Local Bus. The 6 Slot
adds one (1) bridge. These bridges are the communication
paths between the PCI cards and the computer resources.
Most computers allow multiple bridges (and thus PCI buses) to
be correctly configured. Some computers, unfortunately, place
an arbitrary limit on the number of bridge levels that can be
traveled during power-on configuration. Your computer “power-
on-software” should be PCI Specification 2.1 compliant in order
to effectively use a Magma PCI Expansion System. For "fan-
out" and "daisy chained" system configurations, where more
than one PCI expansion system is being used, you should
count all of the bridge levels to your most deeply nested PCI
bus to determine the maximum number of bridge levels that
must be traveled.
3. For easier understanding, the PCI Local Bus should be viewed
as a “Resource Toll road” that runs from the computer CPU
(resource home), through the “Toll Booths” (the PCI bridges),
to the “Resource Users” (PCI Cards). As in the case of a real
Toll Road, the more Toll Booths you have to slow down a
“nanosecond” for, the longer it will take you (your data) to get
from the PCI Card to the CPU and back again. Under most
circumstances the effect cannot even be detected. However,
under other conditions, it can be important to know about.
Fan-Out
For reasons described in bullet #3 above, we recommend using a fan-
out configuration when you need to add successive PCI expansion
systems to the host computer. This addition to the PCI bus hierarchy is
at the "peer" level of other existing expansion buses, thus adding
"breadth" to the PCI bus hierarchy, since these buses will be at the
same hierarchical level within the system configuration.
You may use either PCIe or PCI host cards in your host
computer, depending on available slots and your performance
requirements. You must ensure that you have the
corresponding PCIe to PCI Expansion System, or PCI
Expansion System, chassis to connect with your host card and
support your desired configuration.