Inside CD-R Media 

If you’ve gone out shopping for a CD-R, you’d surely have noticed the many shades and colors of media. Some claim to have a special coating to protect them from heat and scratches, while others talk about maximum compatibility with drives, and some even claim to have gold in their CDs. Well, if this is all confusing, read on. We’ll see what makes a CD-R, how one CD-R differs from another and how data is burnt on a CD-R. So let’s go spinning.

Every CD-R disc has four layers (actually five layers if you count the writing surface). This surface is used for labeling the media after data has been burnt on it for easy identification. It is advisable to use a soft marker to write on it. A ball pen or a pencil can harm the layers underneath it. 

Protective layer



Underneath the writing layer lies the protective layer that is meant to protect the CD from UV radiation, heat, scratches etc. For example, the box of Amkette CD-Rs talks of a “Dura Shield Protective Layer”, which is supposed to protect it from heat, humidity and sunlight. 

Reflective layer



The next layer is also a very important one, called the reflective layer. This layer helps in the reading of the CD-R data when used in different CD-ROM drives. Two types of reflective layers are used–gold and silver. CD-Rs with a gold reflective layer are considered more stable in the long run as gold is one of the least reactive elements in the world. So for things like archiving, storage of data backup etc, gold CDs are supposed to give you an edge. The advantage of a silver reflective layer is that it is more reflective than gold. What this means is that these CDs in theory should be easily read by most CD-ROM drives 

Recording layer



This is where the action is. It is also called the dye layer, because this layer is made of a photo-reactive dye. In order to burn data, your CD writer fires a laser beam in short bursts into this recording layer. Wherever this happens the dye turns into a non-reflective pit. So when the laser of a CD-ROM tries to read that part it gets no reflection, which it interprets as a 0, and the reflective parts as 1. 

It is also this layer, together with the reflective layer that gives the CD-R its distinctive color. So for example if a CD-R is made of a blue-dye layer and has a gold-reflective layer, then it will show up as green. Unlike the reflective layer, the recording layer comes in many different variations, with different manufacturers using different dyes. For example, Acer media uses a phthalocyanine dye where as Verbatim uses its proprietary Metal Azo-recording dye. However unless you are constantly facing a problem with a particular brand of CD-R, you should not worry about this.

Polycarbonate substrate 



And finally, this transparent layer is used to give protection to the layers that lie above it. If you look at the shiny side of a CD-R, then you’ll be looking at this particular layer. 

Sachin Makhija