How CD-ROM Discs Work

How can you look after discs if you don't understand how they are made or work?

To fully understand how to repair a disc, and what can be repaired, you must first understand how discs work. Armed with this information, you will have a clear understanding of what can be repaired and what is heading for the bin!

Although there are many different types of optical discs (CD ROM's) on the market today, they all function on the same general principle. The music, picture and/or computer data they store is in digital form. This means it is comprised of millions and millions of ons and offs or zeros and ones thus the term digital.

Digital information is read from a disc by an infrared laser which projects through the clear protective plastic (Bottom side) of the disc bottom, and is reflected back to a laser reader after ricocheting off the aluminum layer (Top Side).

When the laser projects through the protective layer it reads the encoded surface that is made up of pits and lands that create the ons and offs. By reading the reflected light beam, the disc drive/player decodes this information from the disc thus outputting the information through a TV, computer screen or speakers.

A scratch can deflect the laser beam, resulting in the the information not being read by the player at a certain point on a track. The laser reader then only receives intermittent messages. When this happens the information does not flow thus causing a skip, a freeze in a picture or the non-starting of a CD ROM.

The smallest scratch can affect many lines of information. The most unprotected side of a disk is the topside or the graphics layer which if scratched renders the disk unusable. The reason for this is simple. The laser reader relies on the reflective layer of the Top Side or graphics layer of the disc to reflect the laser back to the reader - when there is a scratch in this reflective layer, the laser will basically go right through the disc, instead of returning down to the reader.

All Players of CD ROM's today are effected in various ways by scratches from the age of the laser as time and usage goes on, the strength of this laser diminishes and light natural scratches can effect the reading of CD ROM's over time where newer, latest released players will have the ability to read through the very same light natural scratch!

Disk's, Disc's, CD's or CD ROMs are all based on the same format that consists of 4 separate but important layers.

Compact Discs begin as a clear polycarbonate disc. The disc's digital information, which allows it to play music, run computer programs or play movies, is stamped on the top of plastic disc.
Next, a reflective foil is placed on top of the digital information. Then a clear lacquer is spread to protect the foil and data. Finally, a graphic or label is printed.


Please note that the sizes of these layers are no more than a strand of human hair. Most CD ROM's can be repaired more than 50 times depending on the depth of the scratches.

If you would like a more detailed explanation of how CD's work, view

Disc Care Tips - How To Fix A Disc

This webpage comes from Disk Doctor