Compact Disks

[JWHooper]

I was curious how does the computer reads all the information included in the compact disk. What kind of technology is included in the computer that makes it possible to read the datas in CDs?

Thanks,

J.

[Tony]

It's a laser and an optical receiver. The CD acts as a (very very long) series of mirrors. If it's a shiny part, computer reads a 1. If it's a dull part, nothing is reflected so 0 is read (or vice versa, I'm not sure).

[Skynet]

A CD is a disc with a single long groove etched as a spiral into the surface. The changes in depth in the groove represent binary data. A laser is aimed at the groove. The reflected laser light has different intensities depending on the depth of the groove. The intensity of the light is converted into an electrical signal via a photosensor.

At this point, there's a stream of binary data going into the CD hardware. Even in the case of a normal audio CD, this isn't pure data - there are some error correction bits built into the stream. The data is passed through a module which performs error correction using these extra bits and spits out the corrected true data. (no more additional error correction bits) What the "true" data means is dependent on the use of the CD. I believe for audio CDs, it's just alternating left/right channels - 16 bits for the left, 16 bits for the right, then repeat.