Active Versus Passive Backplanes
Backplanes have grown in complexity from the simple Industry Standard Architecture (ISA) (used in the original IBM PC) or S-100 style where all the connectors were connected to a common bus. Due to limitations inherent in the Peripheral Component Interconnect (PCI) specification for driving slots, backplanes are now offered as passive and active.
True passive backplanes offer no active bus driving circuitry. Any desired arbitration logic is placed on the daughter cards. Active backplanes include chips which buffer the various signals to the slots.
The distinction between the two isn't always clear, but may become an important issue if a whole system is expected to not have a single point of failure (SPOF). A passive backplane, even if it is single, is not usually considered a SPOF. Active backplanes are more complicated and thus have a non-zero risk of malfunction.
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