Backplanes Versus Motherboards
When a backplane is used with a plug-in single board computer (SBC) or system host board (SHB), the combination provides the same functionality as a motherboard, providing processing power, memory, I/O and slots for plug-in cards. While there are a few motherboards that offer more than 8 slots, that is the traditional limit. In addition, as technology progresses, the availability and number of a particular slot type may be limited in terms of what is currently offered by motherboard manufacturers.
However, backplane architecture is somewhat unrelated to the SBC technology plugged into it. There are some limitations to what can be constructed, in that the SBC chip set and processor have to provide the capability of supporting the slot types. In addition, virtually an unlimited number of slots can be provided with 20, including the SBC slot, as a practical though not an absolute limit. Thus, a PICMG backplane can provide any number and any mix of ISA, PCI, PCI-X, and PCI-e slots, limited only by the ability of the SBC to interface to and drive those slots. For example, an SBC with the latest i7 processor could interface with a backplane providing up to 19 ISA slots to drive legacy I/O cards.
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