The purpose of the backplane is to transfer signals between the attached modules passively. A backplane may carry some additional electric components giving some associated functions. Commonly found on backplanes are; 1)Power input, either as a plug or a screw terminal block, and a light indicating power on and maybe also a power switch. 2) Power regulator which enables the use of a 9 - 18V power supply and reducing the voltage to 5V. 3) Reset circuit and button.

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Above photo; the same backplane with either single 40 female pin header (left) or double 40 female pin header (right).