Abstract: A modular electronic enclosure having a maximum height of 1 U and a width adapted to fit between the rails of a 19 inch rack is adapted to receive up to ten single-width Advanced Mezzanine Cards (AMCs) installed horizontally in the enclosure. Some modules that are not compliant with AMC standards may be installed in the modular electronic enclosure. A backplane, backplane structural support, combined card guide, chassis cover, and chassis bottom cooperate mechanically to provide a stiff, stable enclosure resistant to mechanical flexure. The modular electronic enclosure includes two hot-swappable cooling units which cooperate to establish push-pull cooling airflow. The modular electronic enclosure is further adapted to receive a Power Unit and an MCH. In another embodiment, the modular electronic enclosure includes a backplane with more than one core and has mounting locations and electrical connectors for up to twenty single-width 4 HP electronic modules.