Interface Hard Disk Drive Technology Data is stored in the hard disk's magnetic coating. As the illustration shows, data is organized in sectors, tracks and cylinders. All hard disks feature reserved sectors, which serve as backup in case of a defect in the disk media. These reserved sectors are automatically initiated by the drive logic if a defect is found. A servomotor propels the actuator arm that holds the heads.
Hard disks use a variety of track sizes.
The average seek time is the number of milliseconds the drive requires to position the heads for a request. Generally, the smaller the disk, the shorter the seek time. The seek time is fastest when moving from one track to the next. The slowest seek time is the full stroke between outer and inner tracks. SCSI drives and other hard disks execute the seek command incorrectly, positioning the head near the desired track.