how does a cd writer writes on a cd?

Question

I want know the software protocol. CDROMs and writers connects to pc using IDE bus and reading is through ATA pocket interface but how do they write on the cd? is it using the same protocol or something else? any info or links would be so helpfull to me. thanx.

Answer 1

The CD-RW uses phase shift technology, using a specially created phase shift compound.

The idea behind this is that with this compound the laser can heat it up to melting point at which point the compound turn opaque and the read laser would not be able to bounce back a signal. this then turns into an amorphous state (no crystalline form).
It will cool this way and be opaque until its reheated. In order to get the compound translucent again it needs to be heated again, this time to a lower temperature.
At lower temperatures the phase shift compound will cool in a crystalline form and allow the laser beam to pass through and bounce off the aluminum beneath.

To get the amorphous state the laser heats the compound to around 600C where as to get the crystalline state it only requires heating to around 200C.

When you write data to a CD-RW it stays permanent until its written over. However unlike your hard disk it uses an erase function first.
To erase the section of the disk the write laser simply heats all the area to a crystalline form and then writes whatever data you need onto the now blank piece of disk.

Source (full details) :
http://www.pantherproducts.co.uk/Articles/Storage/cdburner.shtml

regards,
Philip T