It is important that you can distinguish between magnetic and optical storage devices.

Magnetic storage:

Magnetic storage devices store the data on a magnetically coated surface.  They can generally be used many times.  They tend to have a large storage capacity when compared to optical media. 

The main disadvantage is that the data held on these can be damaged if the device is put too close to a strong magnetic field such as a loudspeaker.

Optical storage:

Optical storage devices are read by a laser beam.  Generally they have a more limited storage capacity when compared to magnetic devices.  However, one advantage is that they are more hard wearing than magnetic devices.