The head may be either fixed or movable with respect to the radial direction of the platter.

In a fixed-head disk, there is one read-write head per track. All of the heads are mounted on a rigid arm that extends across all tracks.

In a movable-head disk, there is only one read-write head. Again the head is mounted on an arm. Because the head must be able to be positioned above any track, the arm can be extended or retracted for this purpose. The fixed head and movable head is shown in the Figure 7.8.

The disk itself is mounted in a disk drive, which consists of the arm, the shaft that rotates the disk, and the electronics circuitry needed for input and output the binary data and to control the mechanism.

A non removable disk is permanently mounted on the disk drive. A removable disk can be removed and replaced with another disk.

For most disks, the magnetizable coating is applied to both sides of the platters, which is then referred to as double sided. If the magnetizable coating is applied to one side only, then it is termed as single sided disk.