Since the metal layer is so close to the surface of the label side, pointed objects can easily damage the CD by deforming the metal or exposing it to the environment. Some solvents can also affect lacquer coatings and expose or react with the metal. Once the metal is damaged, the laser cannot read data in the damaged areas. Sometimes a manufacturer will add an additional layer designed specifically to provide more resistance to fingerprints and scratches on the label side of CDs.
One particularly effective modification has been the application of lacquer completely around the edges of the disc. In earlier CDs, moisture had been allowed to penetrate to the metal through unprotected areas of the disc edge. Clearly, it is as important to protect the edges of CDs as it is their surfaces. Such surfaces are of four types:. These layers are applied over the lacquer layer on CDs or over the polycarbonate substrate on a single-sided DVD.
Some discs have an extra coating on which text or logos are printed. In many cases, the lettering appears to be stenciled, but it is not part of the coating; what one sees is the reflected surface of the metal rather than imprinted text or logos. Typically, one can see through this lettered area-and even through the metal-by holding the disc up to light. Because these lettered areas are particularly susceptible to damage, it is most important to avoid writing on or scratching in these areas.
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Sign Up. Follow Us. A DVD player is powered by electricity. DVD players can either be powered by electricity or batteries. DVDs are of the same shape and thickness as CDs, and they are made using some of the same materials and manufacturing methods. A DVD is made up of several layers of plastic that is 1. Each layer is made by injection moulding plastic. This forms a disc that has tiny bumps often called pits arranged as a single very long spiral track of data.
These bumps are where all the data is stored. The bumps and pits on a DVD are coded information. Each writeable layer of a DVD has a spiral track of data. The microscopic dimensions of the bumps make the spiral track on a DVD extremely long. If you could lift the data track off a single layer of a DVD, and stretch it out into a straight line, it would be almost 7. That means that a double-sided, double-layer DVD would have 30 miles 48 km of data! Sign up for our Newsletter! Mobile Newsletter banner close.
Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. The replication house simply uses the metal stamper to imprint the pattern into the plastic coating of all those DVDs. Smaller pits make it possible to store more information on DVDs. What most people find at the local movie rental or video store is called a DVD It's so named because it stores nearly five gigabytes GB of information. The laser that "reads" the information first interprets the data on the top disc and then changes angle to translate the data on the second one.
The DVD works in the same way, except that both the discs are double-sided. Instead of just reading one side for information, the laser reads both sides, something like our old vinyl records.
If you're in the movie rental business that means more long-term profits as you won't have to pay for replacement versions after multiple plays. It has the added advantage that the local franchise won't have to worry about whether you rewind it or not.
In addition, because of special features within the television set DVD player units, it will be impossible for these sets to "read" and play pirated copies of movies on DVD, a problem that has plagued Hollywood's video market abroad. This micrograph shows a commercial die, into which CD manufacturers inject molten polycarbonate plastic to form the pits and lands of an individual disc. DVD digital video disc is a technology based on optical data storage similar to compact disc CD.
Optical data storage is a method of storing digital information 1's and 0's by using light to read the information. Analog information is converted into digital information, which is then encoded onto the disc from the inside edge out.
Digital data are encoded by means of pits on the recording layer of the disc. The pits and the separations between pits, called lands, vary in length to represent the digital information stored in the disc. The pits are arranged in a track that forms a spiral pattern on the recording layer of the disc.
The disc revolves in a circular motion inside the player, while an optical head laser slowly moves outward and remains focused on the pits. The laser beam is reflected back to a detector when it hits the lands, and it is scattered away from the detector by the pits.
The transition between a pit and a land corresponds to a "1" in the digital bit stream. A DVD can store over two hours of video on one layer of the disc. In comparison to the 74 minutes of data that a CD can hold, this capacity marks a vast improvement.
The smallest pits on a DVD are about 0.
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