The CD and DVD are the versions of an optical disk which mainly differ in size and manufacturing method. Generally, a DVD can store more data than a CD, its one of the reason is that CD contain the polycarbonate substrate on only a single side while in DVDs it present on both of the sides.
We have already discussed the construction and working principle of the optical disk in our previous article difference between Magnetic Disk and Optical disk. The CD and DVD work on optical technology where the data retrieved by using light specifically lasers. A laser beam is concentrated into the CD or DVD in order to read the content data stored in the disc in the form of the bits and to write the content.
More Metal layer recording layer position on the disk Top Middle of the disk. Layers of the pits Single Double two-sided Spacing between the loops of the spiral 1.
Can cause an imbalance in spin. 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.
CLIR is an independent, nonprofit organization that forges strategies to enhance research, teaching, and learning environments in collaboration with libraries, cultural institutions, and communities of higher learning. Sign up for news from CLIR. Sign Up. Follow Us. Facebook Twitter Youtube Linkedin Rss. Because of this, you don't need to know anything about CD data formatting to create your own CDs. However, CD data formatting is complex and interesting, so let's go into it anyway.
To understand how data are stored on a CD, you need to understand all of the different conditions the designers of the data encoding methodology were trying to handle. Here is a fairly complete list:. There are several different formats used to store data on a CD, some widely used and some long-forgotten. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close.
Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. How CDs Work. Have you ever wonder how compact discs work? Understanding the CD: Material " ". Understanding the CD: The Spiral " ". Understanding the CD: Bumps " ". CD Player Components " ". A drive motor spins the disc. This drive motor is precisely controlled to rotate between and rpm depending on which track is being read.
A laser and a lens system focus in on and read the bumps. A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track.
The tracking system has to be able to move the laser at micron resolutions. CD Encoding Issues " ". Because the laser is tracking the spiral of data using the bumps, there cannot be extended gaps where there are no bumps in the data track. Improve this answer. Iceking Iceking 1 1 silver badge 10 10 bronze badges. What do you mean by "if it is sideways look for that"? What do the sideways look like? The shiny side is always facing down.
Unless it's facing sideways. Xavierjazz: what does it look like when "it's facing sideways"? Pictures will be nice. My CD player has a clip that allows me to set it on it's edge rather than on the "bottom". There for it is in a vertical position.
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