Compact

DiscsRebecca Martin

May 2005

The CD in General

• Invented in 1980s

• Used to hold music, data, or computer software

• Cheap and easy to distribute a lot of information

Making a CD

• Digital data is encoded on a master disc as bumps

• Changed to binary language of one and zeroes in reading

• Strong laser burns small holes and bumps

Audio CDs

• Smaller and have a better sound quality than phonograph records and audio tapes

CD-ROM's

• Computer data stored on this format

• Stands for Compact Disc- Read Only Memory

• 650 MB

Even More About CD-ROM's

• Can store many images that take up more memory than words

• Can store contents of an encyclopedia with images

How CDs Work:CD Player

• Read out system retrieves sound signal

• Goes to amplifier and pair of headphones

How CDs Work:Laser

• Continually moving outward from center

• As it moves bumps move faster past laser

• Works because of tangential speed

How CDs Work:More About the Laser

• Cannot be extended gaps between bumps

• Incredibly precise to read track

How CDs Work:Bumps or Pits

• Actually bumps on the side that the laser reads, not pits• 1.6 microns away from bump on the left or right of it

How CDs Work:Bumps or Pits Again

• Bumps are 0.5 microns wide, minimum of 0.83 micron long, and 125 nanometers high

• Small dimensions make track very long

How CDs Work:Track

• Lifted and stretched out in straight line, would be 0.5 microns wide and 3.5 miles long

• Incredibly precise mechanism to read

How CDs Work:

Drive Motor

• Spins the disc and controls it to rotate between 200 and 500 rpm (revolutions per minute)

How CDs Work:Laser and Lens System

• Laser and lens system focus in on and read the bumps on the CDs.

How CDs Work:

Tracking Mechanis

m• Tracking

mechanism moves laser assembly so laser beam can follow track

How CDs Work:Layers

• Injection-molded clear polycarbonate plastic• Plastic is impressed with bumps during

manufacturing.

How CDs Work:The Layers Again

• Reflective aluminum

• Thin acrylic layer

• Label

About Me• My name is Rebecca

Martin. I am 13 years old and go to Hanes Middle School. I enjoy playing sports and cheering for Duke. Duke is my favorite college. My favorite sports are soccer and volleyball. I also enjoy talking to my friends and hanging out with them.

Bibliography•“How CDs Work.” U-X-L Encyclopedia of Science. Second Edition, 2002.•Marshall Brain. How CDs Work. HSW MediaNetworks. 29 April 2005. <http://electronics.howstuffworks.com/cd.htm>.•Ian Graham. How Things Work. Italy: Facts On File.1995.•David Macaulay. The New Way Things Work. Boston: Houghton Mifflin Company, 1998.•How Does a CDs Work? 2004. MLK. 5 May 2005. <http://www.copy-cd.biz/technical-area-compact- discs-explained.jsp>.