Abstract: An apparatus having a backplane adapted for coaction with a number of circuit boards arranged in side-by-side relationship and including a number of mutually adjacent and mutually spaced elongated, narrow backplane-related connector fields, each of which is adapted for firm but easily removed mechanical and electrical coaction with a corresponding connector field related to an edge-part of respective circuit boards. A number of first selected backplane-related connector fields are connected electrically to a first bus, and a number of second selected backplane related connector fields are connected electrically to a second bus. The backplane-related connector fields are divided into a predetermined number of groups wherein each group is allotted a part-section of the backplane and wherein the first connector fields of respective groups are joined together and connect to the first bus.