How CD’s Work

How How CD’s CD’s WorkWork

Speros ShepherdSperos Shepherd

20052005

The Anatomy of a CDThe 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 CDThe 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 CDThe 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 CDThe 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 long3.5 miles long

CD Bumps Magnified

The Bumps on a CDThe 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 ComponentsCD 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

CD Player ComponentsCD Player Components• Laser and

lens system focuses in on and reads the bumps

• The tracking mechanism moves the laser.

CD PlayerCD Player

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

CD Player Lasers

Laser Focus of a CD PlayerLaser Focus of a CD PlayerThe 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 TrackingCD 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 FormatsCD Data Formats

A CD-RW (can be edited)

CD Data FormatsCD 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 FormatsCD 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 FormatsCD 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)

SperosSperos• 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 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