An apparatus for cooling the components within an enclosed computer system. The apparatus includes a first compartment (11) containing a power supply (17) and a fan (12), a second compartment (25) containing a variety of electrical components and an air duct (13) containing the computer system microprocessor (14). The air duct directs an air flow from the exterior of the computer system enclosure across the microprocessor to an inlet opening (29) of the first compartment. Holes are provided within the air duct at points downstream of the microprocessor to permit an air flow from the second compartment into the air duct. The fan generates an air stream through the cooling system and exhausts to the exterior of the computer system enclosure.