A computer system, comprising: a chassis configured for mounting in a rack, wherein the chassis comprises one or more chassis air inlets (107; 122) at a front of the chassis and one or more chassis air outlets at a rear of the chassis; one or more circuit board assemblies on the chassis; one or more hard disk drives coupled to the chassis; and one or more air passages under at least one of the hard disk drives, wherein at least one of the air passages comprises one or more air inlets and one or more air outlets, wherein at least one of the one or more air inlets of the one or more air passages is in fluid communication with one or more chassis air inlets and at least one of the air outlets of the one or more passages is in fluid communication with at least one of the chassis air outlets, wherein at least one of the inlets of the one or more air passages is configured to direct at least a portion of the air downwardly into at least one of the passages, wherein the at least one passage is configured to allow air to move from the at least one air inlet of the one or more air passages to at least one of the air outlets of the one or more air passages, and wherein at least one of the one or more air passages is at least partially downstream from the one or more circuit board assemblies on the chassis and is located such that at least a portion of the air in the computer system flows over at least one heat producing component on the one or more circuit board assemblies on the chassis and then into at least one of the air passages under the hard disk drives. a chassis configured for mounting in a rack, wherein the chassis comprises one or more chassis air inlets (107; 122) at a front of the chassis and one or more chassis air outlets at a rear of the chassis; wherein the chassis comprises one or more chassis air inlets (107; 122) at a front of the chassis and one or more chassis air outlets at a rear of the chassis; one or more circuit board assemblies on the chassis; one or more hard disk drives coupled to the chassis; and one or more air passages under at least one of the hard disk drives, wherein at least one of the air passages comprises one or more air inlets and one or more air outlets, wherein at least one of the one or more air inlets of the one or more air passages is in fluid communication with one or more chassis air inlets and at least one of the air outlets of the one or more passages is in fluid communication with at least one of the chassis air outlets, wherein at least one of the inlets of the one or more air passages is configured to direct at least a portion of the air downwardly into at least one of the passages, wherein the at least one passage is configured to allow air to move from the at least one air inlet of the one or more air passages to at least one of the air outlets of the one or more air passages, and wherein at least one of the one or more air passages is at least partially downstream from the one or more circuit board assemblies on the chassis and is located such that at least a portion of the air in the computer system flows over at least one heat producing component on the one or more circuit board assemblies on the chassis and then into at least one of the air passages under the hard disk drives. wherein at least one of the air passages comprises one or more air inlets and one or more air outlets, wherein at least one of the one or more air inlets of the one or more air passages is in fluid communication with one or more chassis air inlets and at least one of the air outlets of the one or more passages is in fluid communication with at least one of the chassis air outlets, wherein at least one of the inlets of the one or more air passages is configured to direct at least a portion of the air downwardly into at least one of the passages, wherein the at least one passage is configured to allow air to move from the at least one air inlet of the one or more air passages to at least one of the air outlets of the one or more air passages, and wherein at least one of the one or more air passages is at least partially downstream from the one or more circuit board assemblies on the chassis and is located such that at least a portion of the air in the computer system flows over at least one heat producing component on the one or more circuit board assemblies on the chassis and then into at least one of the air passages under the hard disk drives.