An electronic computer includes a plurality of printed circuit boards that are slideably mounted in spaced parallel planes within a housing. The housing contains an input/output bus arrangement which is substantially open in the middle. A power supply is detachably mounted to the housing in such a manner as to automatically connect to the input/output bus arrangement when it is secured in place. The power supply includes suction fans which draw ambient air in through the front of the housing over the printed circuit boards, through the open portion of the bus arrangement and hence over critical portions of the power supply. The air is initially drawn through perforated openings in a hinged control panel in one preferred embodiment. In another preferred embodiment, the air is drawn through a stationary member at the front of the housing.