How a CDROM Works

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How a CD-ROM Works

• Bill Holmes
• Chandler-Gilbert Community College

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Overview

• CD is standard for installing computer programs
• Uses CD-ROM media (Compact Disk Read Only Memory)
• 650 Mb. capacity compared to 1.44 Mb. for floppy
  disks
• Pits (holes) and Lands (plateaus) store the data
  (1s and 0s)

http//entertainment.howstuffworks.com/cd1.htm
http//www2.h-net.msu.edu/filmhis/resources/CD-RO
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Parts Overview

• Tray motor
• Ejects and pulls in CD tray
• Read head
• Shines light on CD and reads reflection
• Spin motor
• Spins the CD at various speeds

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Reading Data From a CD

• Laser shines light on disk
• Pits and lands reflect light differently
• Reflected light is picked up by sensor
• Sensor changes light to electrical signal for the
  computer
• Motor moves the head to read all parts of the
  spinning CD.

Demo http//entertainment.howstuffworks.com/cd2.h
tm
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CD Finish

• CD spins between 200 and 500 RPM depending on
  position of the head
• Faster near center
• Slower near edge
• That way data comes off disk at same rate
• Demo bottom of http//entertainment.howstuffworks
  .com/cd2.htm
• Clean with soft damp cloth
• Handle by edges only, dont touch surface

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