magneto optical disc (MOD)
Magneto-optical discs, Magneto Optical Disc (MOD), consist of a thin layer of vertically magnetized material sandwiched between a transparent polycarbonate protective layer and a reflective layer.
The storage is magnetic and can be performed only after heating the working area by a laser. According to the method, the magnetic information layer, which is initially uniformly aligned, is exposed to a magnetic field that causes a change only when the coercive forces of the magnetic material are lowered by heating. The effect of the magnetic field and the heating light beam occurs at defined locations and remains after cooling. This process can be bit-selective.
The data is read using the magneto-optical Kerr effect with a laser beam that is reflected differently from the magnetized and non-magnetized areas.
MO discs are floppy disks in 5.25" (12 cm) and 3.5" (8 cm) with storage capacities of 16.7 GB (12 cm) and 2.3 GB. The MO disc can be overwritten any number of times (several 100 million times). The write and read speeds are many times higher than those of DVDs. Since MO discs are not sensitive to light or temperature, they can store data for much longer than DVDs or compact discs and can also be used in archiving.