Abstract: A modular computer system, for example a high density server system, includes an enclosure for receiving a number of computer system modules. A number of information processing modules, for example server blades, are receivable at a first face of the enclosure. A number of support modules of a first type, for example combined switch and service processor modules, and a number of support modules of a second type, for example power supply modules, are receivable at the second face of the enclosure. In order to provide cooling air to the first type of support modules, which are temperature sensitive, a plenum chamber provides a flow path for cooling air that bypasses the information processing modules. For the second type of support module, which is not as temperature sensitive, a flow path for cooling air is provided that passes through the information processing modules.