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
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
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,
Disc Care Tips -
How To Fix A