How CDs, DVDs, and Video Game Discs are Made and Processed. A project on materials and elements used in making one of mankind’s most used discs by Matthew Jefferson

Overview Compact Discs (CDs) are one of the most used items on the market today next to the Apple iPod. People think that the CD is easy to make and that all you do is stick in the disc into a computer and it plays. Well that is partially true. Kind of. Do these look familiar? These are the systems (or formats) of the kinds of discs that I am going to present to you. First off, the history of the CD…

The History Of The CD In 1979, the Philips and Sony corporations joined forces to coproduce the CD-DA (Compact Disc-Digital Audio) standard. Philips had already developed commercial laserdisc players, and Sony had a decade of digital recording research under its belt. The two companies were poised for a battle the introduction of potentially incompatible audio laser disc formats when instead they came to terms on an agreement to formulate a single industry-standard digital audio technology. Philips contributed most of the physical design, which was similar to the laserdisc format it had previously created with regards to using pits and lands on the disk that are read by a laser. Sony contributed the digital-to-analog circuitry, and especially the digital encoding and error-correction code designs. In 1980, the companies announced the CD-DA standard, which has since been referred to as the Red Book format (so named because the cover of the published document was red). The Red Book included the specifications for recording, sampling, and above all the 120mm (4.72") diameter physical format you live with today. This size was chosen, legend has it, because it could contain all of Beethoven's approximately 70-minute Ninth Symphony without interruption. After the specification was set, both manufacturers were in a race to introduce the first commercially available CD audio drive. Because of its greater experience with digital electronics, Sony won that race and beat Philips to market by one month, when on October 1, 1982 Sony introduced the CDP-101 player and the world's first commercial CD recording Billy Joel's 52nd Street album. The player was first introduced in Japan and then Europe; it wasn't available in the United States until early In 1984, Sony also introduced the first automobile and portable CD players. Sony and Philips continued to collaborate on CD standards throughout the decade, and in 1983 they jointly released the Yellow Book CD-ROM standard. It turned the CD from a digital audio storage medium to one that could now store read-only data for use with a computer. The Yellow Book used the same physical format as audio CDs but modified the decoding electronics to allow data to be stored reliably. In fact, all subsequent CD standards (usually referred to by their colored book binders) have referred back to the original Red Book standard for the physical parameters of the disc. With the advent of the Yellow Book standard (CD-ROM), what originally was designed to hold a symphony could now be used to hold practically any type of information or software.

How CDs are made with what they are made with and why This is what CDs are made with and why… A disc is created from molten polycarbonate (Because it is cheap to buy and reliable to use) and digital information is stamped on the top of the disc, while it is still near melting point, using a die with microscopic bumps. These bumps are known as “pits and lands”. After the information is molded into the poly- carbonate, a reflective foil layer is applied using a process called sputtering or wet silvering. This layer reflects the laser back to the player (so it can give the signal to play). So it’s integrity is extremely important. The layer is usually silver, but can be made of gold or platinum. A clear lacquer coating is applied to seal the reflective layer and prevent oxidation (this means it will not have a chemical reaction to the oxygen). This layer is very thin and offers little protection from top side scratches. Finally the artwork is screen-printed on the top of the disc (to make it look awesome when you stick in the disc player)

Pits and Lands Pits and Lands are imprinted into the disc to indicate a one or a zero. A laser beam is sent from the player to the disc and the reflective layer reflects it back to the reader and the ones and zeros are translated by the player. Recordable discs have a photosensitive dye type layer instead of the stamped information layer. This layer, when exposed to a certain light, will make an impression of a pit into the layer. The same also applies to double discs just on both sides.

HOW CDs ARE READ Although there are many different types of optical discs, 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 of ones and offs or zeros and ones – thus the term “digital”. Digital information is “read” from discs by an infrared laser which projects through the clear protective plastic of a disc bottom, and is either reflected or not reflected back to the laser reader. The encoded surface is made up of microscopic pits and lands which create the ones and offs. By reading the reflected light beams, a disc drive decodes the information on a disc. A scratch deflects the laser beam off track and information is never received by the laser reader. The smallest of scratches can effect many lines of data.* The most unprotected side of a CD is the top or graphic side!

How CDs break Scratches are one of the worst enemies of data on an optical disc. Where a scratch occurs determines if your disc is repairable. Data resides on the top side of the polycarbonate disc. It is extremely important to protect this side of the disc. Manufacturers, however, leave this side highly exposed. A scratch on the top, through the foil or the stamped data, will result in lost data and a non-repairable disc. A scratch that occurs on the bottom side of a disc, however, may be resurfaced and polished out. The depth of the scratch will determine the success of the repair. Keep an eye on these scratches during normal use and get them repaired.

Thanks To… repair.php Thanks goes to Michael Kennedy, VP of Sales at Compact Disc Repairman, Inc. Located at 7942 West Bell Road, Glendale, AZ repair.php compact-disk-made/ Thanks to Mohsin Tiwana, Fahad Tiwana and Saad Tiwana at RealityPod.com which is somewhere in India compact-disk-made/