The electronic equipment of a computer system including electronic cards, power supplies, peripheral units, cooling units and internal and external cables are compactly packaged within a small enclosure in a way which permits sufficient airflow from front to rear of the enclosure. The enclosure includes a pair of rail members located at the rear which have a plurality of mounting positions for attaching a corresponding number of modular shelf members which are angled to permit the flow of air through established airflow paths. The rail and shelf members collectively form a bulkhead structure. The rail members are offset from the sides of the frame so as to form vertical channels on each side. The channels are used for retaining external cables which plug into connectors mounted on the shelf members and are distributed so as not to interfere with airflow.