Formatting a hard drive lays down an exact pattern of tracks that are the same distance from the spindle around which the platters rotate. Each group of tracks forms the shape of a cylinder. Tracks form concentric circles beginning with track 0 at the outer edge of the disk. How close together these tracks are placed on a platter determines the amount of data it can hold. Each track is divided into sectors , which are identified by the side of the disk on which they are located, their track number, and the sector number within the track.
Computers use a file system to organize the files on a disk.
This is one reason why data saved to a disk formatted for one system cannot be read by another system. The FAT, FAT32, and NTFS file systems rely on clusters as an integral part of data storage. A cluster is the smallest allocation unit in these three file systems. The table is much like a road map that represents whether each cluster of a disk is free or allocated to a file. As a drive motor spins the disk at 300 revolutions per minute, a stepper motor moves the actuator arm in a straight line, to position the heads precisely at a selected sector and track.