How CD’s Work

1. How CD’s Work Speros Shepherd 2005

2. The Anatomy of a CD • Piece of simple plastic- 4/100 of an inch thick • Injection-molded, clear, polycarbonate piece of plastic • Has microscopic bumps arranged in an extremely long spiral track Complex CD Layers

3. The Anatomy of a CD • Thin, reflective, aluminum layer covers the bumps. • Thin acrylic layer is used to protect the aluminum layer Simple Layers of a CD

4. The Spiral of the CD • Spiral data track always starts in the center • 0.5 microns wide • 1.6 microns separating the individual tracks • Micron= millionth of a meter The Basic CD Spiral

5. The Bumps on a CD • Bumps make track long because of the small dimensions • If stretched out track would be 0.5 microns wide and 3.5 miles long CD Bumps Magnified

6. The Bumps on a CD • Bumps- 0.5 microns wide, 0.83 microns long, 125 nanometers high • Nanometer- billionth of a meter • Bumps look like pits on the aluminum side. CD Bumps Magnified

7. CD Player Components • Drive motor spins the CD • Drive motor rotates between 200-500 rotations per minute • Laser moves at micron resolutions Parts of a CD Player

8. CD Player Components • Laser and lens system focuses in on and reads the bumps • The tracking mechanism moves the laser. CD Player

9. Laser Focus of a CD Player • The technology forms data into understandable blocks (on an Audio or CD-ROM) • CD player- focuses laser on the data track Different Focuses of a CD Laser

10. Laser Focus of a CD Player • “lands”- aluminum layer • opto-electronic sensor: detects change in reflectivity CD Player Lasers

11. Laser Focus of a CD Player The electronics in the drive interpret the reflectivity changes to read bits that make up the bytes. Laser stages: passes through polycarbonate layer, reflects off aluminum layer, hits opto-electronic device that detects changes in light. How a Laser Focuses on a CD

12. CD Player Tracking • Laser beam centered on data track system continually moves the laser outwards. • spindle motor slows the speed of the CD so that the bumps travel past the laser at a constant speed. (data comes off at a constant rate)

13. CD Data Formats • 2 most common: CD-DA (audio CD), CD-ROM (computer data).These are both widely used. Data is converted into electrical pulses by laser reflections. A CD-RW (can be edited)

14. CD Data Formats • modifications to the CD have to be made for you to burn data on it. (CD-RW have no bumps) A CD-RW (can be edited)

15. CD Data Formats A clear dye layer covers the CD’s mirror.The laser that writes the data to the disc heats up the dye layer to make it opaque. A CD-R (cannot be edited, just read)

16. CD Data Formats • The dye layer must become transparent for data to be written. The data can be changed or rewritten when heated or cooled. A CD-R (cannot be edited, just read)

17. Speros • I am 13 years old and in the seventh grade. • I like playing and watching football • I am Greek. • I like going to parties, but NOT dancing.

18. Bibliography • Brain, Marshall. How CD’s Work. How Stuff Works. 25 April 2005. <http://electronics.howstuffworks.com/cd1.htm>. • How Do Cd’s Work. CDMan Disc Manufacturing. 28 April 2005. <http://www.cdman.com/technical/howdocdswork1.html>. • How Do CD-RW’s Work? How Stuff Works. 2 May 2005 <http://electronics.howstuffworks.com/question655.htm