Magnetic storage uses an arrangement of magnetic impressions on a disk or tape, while optical storage uses pits in the surface of a material. Of the two, optical data storage is far more durable for a number of reasons.
Physical Differences
The pits in the surface of an optical storage disk, such as a CD or DVD, are far less susceptible to physical damage or degradation than the matrix of ferrous particles in a magnetic storage tape or disk. In addition to this, optical storage disks need not be kept in tightly sealed containers as they are not susceptible to contaminants such as fingerprints or dust.
Degradation
The presence of strong magnetic fields, such as those due to speakers or other hardware, can disrupt the delicate magnetic patterns stored on magnetic storage media. This can result in erasure of entire sections of the data stored on such media.
General Weaknesses
The magnetic impression on a magnetic tape or drive inevitably begins to degrade after a period of time; a period much shorter than the shelf life of optical storage media. The reading process for magnetic media also conspires to degrade the quality of data over many read cycles.
