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.

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.

Fig 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.

Fig 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 like a 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.The finished 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

Fig 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 consists of 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.