System having backplane performance capability selection logic

A system having a plurality of printed circuit broads each one having an electrical component thereon. A backplane carries a signal indicative of a performance characteristic of the electrical components on the plurality of printed circuit boards plugged into such backplane. The performance characteristic may be, for example component speed, operating protocol, etc. System start-up is interrupted upon detection of such incompatibility. After start up, upon plugging an additional printed circuit broad having an electrical component thereon with an operating incompatible with the electrical components on the plurality of printed circuit boards into the backplane, the electrical component on such additional printed circuit will not be electrically coupled to the electrical component on the additional printed circuit board from the electrical components of the plurality of printed circuit boards.