Which Backplanes contain no circuitry at all?

Answer 1

Backplanes have grown in complexity from the simple ISA (used in the original IBM PC) or S-100 style where all the connectors were connected to a common bus. Because of limitations inherent in the 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 very clear, but may become an important issue if a whole system is expected to have no single point of failure. A passive backplane, even if it issingle, is not usually considered a SPOF. Active backplanes are more complicated and thus have a non-zero risk of malfunction.