www.whyville.net May 21, 2006 Weekly Issue

Guest Writer

How Do My CDs Work?

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Hey! Sam77777 here to tell you all how those little flat discs we listen to and play with work and entertain us!

As most of you Whyvillians reading this know, CDs allow us to listen to our favorite music and play our favorite games. But do any of you know how they really work? Well I'll tell you!

CDs or compact discs, are an easy way to listen to music, unlike cassette tapes that were hard to play and could easily come apart or unravel. They were also harder to store because their cases were thicker and bigger. You needed to have a big cassette player just to play a small, square cassette.

CDs are different though! They are flatter and easier to store! They are less likely to get ruined or unravel (because there is no ribbon). And if they do get scuffed or scratched, they are much easier to fix. They are able to be played in a smaller CD player.

Have you ever looked at the side of a CD? It just looks shiny and smooth, but behind that, there are four different layers inside. The top layer is the label which tells you the title of the CD or the name of the artist. The second layer is acrylic (acrylic is a glass-like plastic that can fuse together with another substance when heated and becoming hard when cooled). The third layer is aluminum, and the fourth and thickest layer is polycarbonate plastic (a type of plastic that is light weight and flexible). All of that is put into a tiny disk that is 1.2 mm (millimeters) thick. Wow, those layers must be very flat!

On the polycarbonate plastic layer, there is a spiral of data (that's why the CD spins!) which has the song or game data that you are listening to or playing with. This spiral circles the center of the CD. This spiral data track is very tiny so the CD can fit as much data as needed and still stay less than 12 cm wide.

One data track is 0.5 microns (a micron is one millionth of a meter) wide and has 1.6 microns between each track. On every track there are tiny little bumps that are 0.5 microns wide (as wide as each track) and 0.83 microns long. What is even more amazing is how high these bumps are. Each bump is 125 nanometers high, which is 125 billionths of a meter! That's so tiny you can't even see it! These tracks would be 3.5 miles long if you took them off the CD and stretched them out.

If these tracks are so tiny, then a CD player must be pretty high-tech to be able to read it. The parts of the CD player that read and help read the bumps are the disc drive, disc drive motor, laser lens, and laser pickup assembly. The disc drive locks the CD in and helps it stay in one place and the disc drive motor, if you haven't already guessed, turns the the disc drive so the data track can be read. The laser lens reads over the little bumps and plays the data it reads so you can hear the music. The laser pickup assembly moves the laser lens back and forth to read the data tracks.

So that's how your CD works! Now the next time you're listening to your favorite song, think of how you're hearing it! Remember that those little bumps can be damaged easily so take care of your CDs and they will continue to entertain you!

This is Sam77777 signing off!


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