An array disk system includes a plurality of disk drives having disk-like recording media each having a surface divided into a plurality of zones and the data capacity per track is varied in each zone. The plurality of disk drives are divided into a plurality of groups. Reading/writing heads of the disk drives are positioned to access tracks having different zones on the disks in each zone on the basis of a cylinder address designated by a host system. Data transferred from the host system is divided in accordance with a ratio of data capacities of the tracks to be accessed and is recorded in each of the disk drives simultaneously.