The mini disk was a truly weird system. Half way between a cassette and a CD. CD used a laser to to reflect off bumps(or dyes in some varieties) on the disk to get a signal, and a cassette would use a metal head to detect magnetization along the tape to get a signal.
The mini disk used a laser to read the magnetization around the disk. Essentially the magnetism would change the polarity of the light as it bounced off, and by measuring what the polarity of the reflected light is, the device got the signal.
Writing to the disk was also wild, as unlike the cassette, the magnetic field of the disk couldn’t just be changed by putting it next to a strong magnet like. Instead, it had to be heated up before the magnetism could be changed, this heating was done with the laser, and was very precise compared to a cassette’s method. This meaning way more information could be squeezed on to the disk than on a cassette.