Abstract: A gas filtering arrangement is described for a magnetic disk file consisting of a closed housing surrounding the magnetic disks. A bearing mounted in a wall of the housing carries a drive shaft upon which the disk (or disks) and a gas impeller are mounted. The impeller pumps gas through a main filter, located within the housing, to clean the gas. The air flow due to the impeller and the disk is arranged to maintain a positive air pressure adjacent the bearing to prevent gas entering the housing through the bearing. A breather filter within the housing connected to the exterior of the housing by a breather aperture is arranged so that during operation a negative pressure is applied to the breather filter to prevent gas leaving the housing through the breather filter.