With the Napster boom in the late 90s came a market for cd burners.Record
companies began to lose millions due to this while electronic companies
began to cash.People needed a way of transferring their music. Sales of cd
burners, CD-R (cd-recordable) and CD-RW (cd re-writeable) skyrocketed.

Today a CD-burner comes as standard in a modern PC.DVD burners are not
uncommon in modern PCs either. Prices for cd burners are falling
dramatically because of mass production due to high demand.

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CDs store music and other types of information
uses the binary numeric system(only counts with 1s and 0s).Tiny bumps are
arranged in a continuous track.The track measures .5 of a micron
wide(millionth of a metere) and 3.5 miles long if stretched out.To collect
this information the cd player shines a laser on the surface of the cd.When
it passes over a flat area of the cd the player recognises it as a 1.When
the laser passes over a bump it is recognises it as a 0.This data is then
processed by the cd player and is heard as digital sound.

picFig 1.

To record a cd a high powered laser is used.A layer of photo-resistant
material is applied to the cd.The laser is shun onto this material with
high intensity which in turn creates bumps on the surface of the cd.Then an
aluminum coating is placed over the photo-resistant material.This allows
the laser to be reflected back onto a sensor once the laser goes over a
bump.A plastic layer is then placed over the cd.This is for protection
against scratches and dust.Other more protective layers have been invented
but have not been put into production due to cost.

picFig 2.

During the 90s floppy discs were the only way of extracting information
from a computer.Their memory was limited(only 1MB).With this high demand CD-
Rs(CD Recordable discs) were created.Instead of using bumps likea
traditional cd a reflective metal layer is put on top of a photo sensitive
dye.Then a light of a particular intensity and frequency is shun onto the
cd.This reacts with the photosensitive dye and darkens it.Thefinished
product gives the same effect as a conventional cd with bumps would.A laser
is shun onto the reflective surface and is reflected back.However when the
laser passes over the areas that have been darkened the laser is not
reflected back thus giving the same effect as the bumps.These CD-Rs are not
without their flaws though.Because they do not have bumps not all cd
players will play them.Another big drawback is that once you have recorded
over them you cannot record over them again
picFig 3.

Different cd burners can burn at different speeds.On different burners you
will see different x symbols.1x means that it would take 1 hour to record a
1 hour cd.2x means that it would take 30 minutes to record a 1 hour cd and
so on.The faster the speed of the burner the more accurate the laser has to
be.Cd burners have both read and write lasers.The write laser is a lot more
intense and of a higher frequency then the read laser.The photo-resistant
layer on a cd-r will not be disrupted by the read laser.This means that a
recorded cd can be played in a normal cd player
CD-RW(cd-rewritable discs) are discs that can be recorded over again.They
use a phase-change technology.A chemical compound which consistsof
tellirium and indium.A high powered laser focuses on the cd changing the
compound of the material.This is done with precise accuracy and can be read
in the way that CD-Rs are read.The compound is heated to about 600
Celsius.If the user wishes to re-write the cd the burner simply reheats the
disc.CD-Burners come as standard in most modern day computers.


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