How CD’s Work Speros Shepherd 2005

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

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

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

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

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

CD Player Components Drive motor spins the CD Drive motor rotates between rotations per minute Laser moves at micron resolutions Parts of a CD Player

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

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

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

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

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) CD Player Tracking Laser beam centered on data track system continually moves the laser outwards.

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. CD Data Formats A CD-RW (can be edited)

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)

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)

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)

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.

Bibliography Brain, Marshall. How CD’s Work. How Stuff Works. 25 April How Do Cd’s Work. CDMan Disc Manufacturing. 28 April How Do CD-RW’s Work? How Stuff Works. 2 May 2005 < 55.htm