Air flows along two paths. In the first path, which is used to cool the power supply unit, air flows from the front lower part of the power supply unit, through the power supply unit air filter, along the lower part of the power supply unit, then out the rear of the power supply unit. In the second path, which is used to cool the cards and drives in the server, air flows from the front upper part of the power supply unit, through the main air filter, up through the fan trays, up through the cards and drives, then out the upper rear part of the server.