eli5 How do rewritable cds 💿 work?

Question

I know how normal cds work, they are basically aluminum molds of data in binary. So how do rewritable ones get erased and reformatted?

In: 80

Answer 1

There is a metal film inside rewritable discs. It can be melted with a laser and then solidifies. If a low power laser is used, it turns into a crystalline structure that is shiny. But if a high power is used it becomes an amorphous solid that absorbs more light. Thus it is possible to create a pattern between light and dark that a reading laser can detect. The dark spots can still be melted to erase the disk.