How a CD-ROM Works

Bill Holmes

Chandler-Gilbert Community College

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.htmhttp://www2.h-net.msu.edu/~filmhis/resources/CD-ROM.gif

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

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.htm

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, don’t touch surface