A personal computer housing has a plurality of air intake openings located around the sides and front. A fan is mounted at the rear of the housing and sucks or draws coolant air through the intakes and exhausts the air to the rear. A bulk power supply is mounted along one side of the housing and is cooled by air flow through adjacent intakes. A plurality of I/O or expansion cards are located along the opposite side of the housing and cooled by air flowing through adjacent side intakes. A plurality of system cards including a processor card and memory cards, are located in parallel, rearwardly extending rows directly between at least some of the front intakes and the fan. A DC/DC regulator card is mounted over the system cards and has a heat sink provided with rearwardly extended cooling fins aligned in the direction of air flow from front to rear.