this ppt is about short overviwe of Optical Discs which is basicaly type of storage.this is baisd on othantic data with no error.

1. Optical Discs :
First invented by James Russell.
In 1960 .
It is a form of removeable storage .
It includes CDs ,dvds and Blue-ray disc .
A laser beam is used to read and write data on optical disc.
Laser create pits on its surface.
Data stored in a single track that seprats from the center of disc to the edge of disc.
Many computers has optical disc Reader/ Drives.
Optical drive reads data by focusing laser beam on the surface of the disc.
It detects the presence of a Pit.
Pit not reflacts light and indicates binary diget 1.
A bead rotates discs very fast 200rpm-4000rpm.
CD store 700MB ,DVD store 4-16GB,Blueray store 50-100GB.
Its size is 4.7 inches.
Data store in single track their distance b/w is known as Track Pitch.

2. • Cabonat.
• No physical contact occur.
• More data stored by decreasing size of Pits and decreasing wave light of laser
beam and Track Pitch.
•
• Structure & working :
• A disk made of three or four layers.
• 1. Plastic Base.
• 2. Alominum coted layer/Film.
• 3. Prolsctive Poly Carbonates.
• 4. matel ally or Carbon & Grafite or dye ink.
•
• A laser hit on the surface of the disc and create a Pit which does not reflect light
and absorbe it so no signal Resent on light sensing diode So sends digital sigmal
of (0) on computer.If reflacted light sensing diode sends a signal at one(1) .