The processes of reading from and writing to a phase-change optical disc. How does the performance and areal density of these discs compare with magnetic disks?

This question is incomplete, here is the complete question:

Describe the processes of reading from and writing to a phase-change optical disc.

How does the performance and areal density of these discs compare with magnetic disks?

Check the explanation

Explanation:

1) A phase-change optical disc is encrusted with an amorphous or crystalline kind of material. A bit area in the amorphous status is changed to a crystalline status while smiting it up to a specific temperature with a laser.

Converting the bit area in the crystalline state to the amorphous state is done through heating it to the material's melting point.

2) The Phase-change optical discs have not so quick access rate than the magnetic disks because longer time is involved to heat a bit with a laser than to change its magnetic polarity.