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Drag a word to its definition. You have answered 0 of 3 questions correctly and your score is:. Want to add a little wonder to your website? Help spread the wonder of families learning together. We sent you SMS, for complete subscription please reply. Follow Twitter Instagram Facebook. How do CDs work? What does CD stand for? What are CDs made of? Wonder What's Next? Find a friend or family member to help you explore the following activities: How popular are CDs today? Can you still find them easily?
Ask an adult friend or family member to take you on a field trip to a local computer or electronics store. Which technologies seem to be replacing these forms of storage and media? Talk with a friend or family member about the changing history of music media. Over the years, we've gone from albums to reel-to-reel tapes to eight-track tapes to cassette tapes to CDs and now digital files. Is digital music here to stay? Or will there be yet another revolution to something else entirely?
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Join the Discussion. Olivia- Buddies 4 Fan Feb 4, We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD not to scale looks like this:. A CD has a single spiral track of data, circling from the inside of the disc to the outside.
The fact that the spiral track starts at the center means that the CD can be smaller than 4. CD business cards hold about 2 MB of data before the size and shape of the card cuts off the spiral. What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0.
A micron is a millionth of a meter. And the bumps are even more miniscule The elongated bumps that make up the track are each 0. A nanometer is a billionth of a meter. Looking through the polycarbonate layer at the bumps, they look something like this:. You will often read about "pits" on a CD instead of bumps.
They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps. The incredibly small dimensions of the bumps make the spiral track on a CD extremely long.
If you could lift the data track off a CD and stretch it out into a straight line, it would be 0. To read something this small you need an incredibly precise disc-reading mechanism.
Let's take a look at that. The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:. Inside the CD player, there is a good bit of computer technology involved in forming the data into understandable data blocks and sending them either to the DAC in the case of an audio CD or to the computer in the case of a CD-ROM drive.
The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light.
The bumps reflect light differently than the "lands" the rest of the aluminum layer , and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes. The hardest part is keeping the laser beam centered on the data track. This centering is the job of the tracking system.
The tracking system, as it plays the CD, has to continually move the laser outward. As the laser moves outward from the center of the disc, the bumps move past the laser faster -- this happens because the linear, or tangential, speed of the bumps is equal to the radius times the speed at which the disc is revolving rpm. The change in the dye creates the equivalent of a non-reflective bump. This is a permanent change, and both CD and CD-R drives can read the modified dye as a bump later on.
It turns out that the dye is fairly sensitive to light -- it has to be in order for a laser to modify it quickly. Therefore, you want to avoid exposing CD-R discs to sunlight. 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 do CD-R discs work?
Updated: May 12, They have been used for recording audio tracks up to 80 minutes.
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