Why is optical disk is first than magnetic disk?

Question

Why is optical disk is first than magnetic disk?

Answer 1

I don't know what "is first than" means, but I guess you are asking why CDs are better than the older magnetic disks.  A couple of reasons.  The optical disk data is more permanent.  Magnetic disks can lose their integrity, especially when accidentally exposed to a strong magnetic field.  But the main reason CDs are better is because for a given size, they can store much more data.