Where's the actual aluminium layer on CD's?

[guferr]

As someone who have already studied about optical media for a long time, including different surface geometries, materials, optical lasers and head systems:

The classic aluminium layer that gives the CD's their classic appearance is not the one that contains data?

I'm asking that, because an old audio CD i have had a parched aluminium layer, and it lost several pieces of it, making voids on the layer.

I first thought it was dirt, and as i tried to remove the "dirt", more pieces of aluminium got off from it.

You can clearly see the other side through the voids made on it.

The disc had 14 tracks, it is almost full of data, looking in the data side, you can see that at least 75% of it is full.

Then i put it on my drive, and tried to rip it, and... Success???

It worked, all the 14 tracks were read perfectly, i listened to all the songs, there was no error on them.

So, what's up with this? Isn't that alluminium layer the actual layer where the data resides?

Is there another aluminium layer that is still in there, with the data, but it's so thin that i can't see?

I always belived that the data is written on that reflective alimium layer, and that's why all discs had that classic look.

I'm confused now.

 

[cklaubur]

The aluminum layer acts as a reflector for the laser. No data is actually stored on it. The data is stored in one of two ways, based on manufacture. A pressed CD stores data in pits in the plastic layer of the CD, while a burnable CD stores data in darkened spots in a chemical layer.

As long as the pits or darkened spots can be read by the laser, the CD is readable. I personally wouldn't trust that CD anymore, though.

Casey

 

[guferr]

The aluminum layer acts as a reflector for the laser. No data is actually stored on it. The data is stored in one of two ways, based on manufacture. A pressed CD stores data in pits in the plastic layer of the CD, while a burnable CD stores data in darkened spots in a chemical layer.

As long as the pits or darkened spots can be read by the laser, the CD is readable. I personally wouldn't trust that CD anymore, though.

Casey

But without the reflective layer, how could the drive read the data on the other layer then? Yes, it's a pressed CD, but without the reflective layer, the head shouldn't be able to read the data on those parts. But it did.

Maybe the light was reflected on the inner part of the drive? It is a laptop drive, and the CD fits very tight on the drive, and its inside is reflective (it's made of aluminium), but it is far not as polished as the aluminium layer of an CD.