Abstract: Data track positioning information for data tracks on a stack of recording disks is provided by servo information pre-recorded on one surface of the stack. In addition, each data track on the remaining surfaces of the stack has servo information relative to that track pre-recorded in sectors around the track. Track following operations are controlled in a closed loop servo system using on-track position information derived from the sectored servo tracks associated with the track being followed. The bandwidth of the position error signal derived from the sectored servo information is increased by adding high frequency components obtained from the continuous servo information on the servo surface. Track access operations are controlled using track crossing information derived from the pre-recorded servo information on the servo surface.

Abstract: A positioning system for data storage apparatus in which a magnetic transducer is positioned relative to data tracks on a moving record member by means of a closed loop servo system. Improved velocity control information is provided to the servo system by pre-recorded servo tracks read by a single servo head forming part of the closed loop system. Each servo track consists of a plurality of servo cells, alternate ones of which are laterally displaced by half a track width. A position reference signal is prerecorded in each cell at a point which is predetermined to permit the signal to be sensed by the single servo head independently of any other detectable signal. Accordingly, a position error signal derived from displaced cells is always 90.degree. out of phase with the position error signal derived from undisplaced cells.

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.