how do reqritable cd's work?

[The_Thinker]

Well, there was a thread on how general cd's work, but then i wondered how would the rewrittable cd's work? Could someone clear it up for me?

[Cliff_J]

There is a dye in the plastic of the recordable CD. The dye is normally transparent and the laser can go right through it and reflect. When the disc is 'burned' the dye is heated and becomes opaque so the laser is no longer reflected in those areas. The dye is only changed opaque in those areas to represent the pits needed to represent the data.

Cliff

[HallsofIvy]

But the question was about REWRITEABLE CD's.

Is the dye made transparent again? How?

[Cliff_J]

Oops! Here, I'll search...

http://electronics.howstuffworks.com/question655.htm

and there is a link to describe the materials in more detail.

Cliff

[The_Thinker]

thx.. for the reply

[HallsofIvy]

I must confess that when I saw "reqritable", my first thought was "regrettable".

Yes, I have heard a number of regrettable C.D.s!

[ceptimus]

The explanation I saw was that a plastic was either heated by the laser and allowed to cool quick, which made shiny crystals, or heated and allowed to cool slowly, which made an amorphous, less shiny area.

This sounds vaguely believable, till you add in the fact that there are tens of thousands of such write events per second, and the regions are tinier than the point of a needle, and it all happens on a disc spinning at several hundred or thousand of revs per minute.

So I prefer to believe that it is a form of magic. That seems much more believable.

[pikapika!]

I read that the chemicals in a rewritable can only be changed 100 times.