HOW CD'S WORK

CD:
Compact Disc.

Shiny on one side laser beam can bounce off the disc and read the information stored on it

Dull on other side has a label and tells about what the CD

Layers of CD:

Lacquer layer:
Clear liquid that is painted on a surface and dries hard and shiny.

Before invention of CD how the data is stored:
On plastic LP (long-playing) records and cassette tapes.

Also known as:
Optical storage devices.

Invention:
James Russell on 17 August 1982.

Compact:
Joined or packed together.

Disc:
Flat circular object.

Compact disc:
Device used to store digital data.

Digital data:
Form of audio, video or computer information.

Thickness:
1.2 mm

How much CD weighs:
15 to 20 grams.

How data is stored on CD:
Series of tiny indentations known as pits encoded on spiral tracks.
Areas between pits known as lands.

How data is burned on to surface of disk:
Laser beam inside CD drive.

Material of CD:
99% base layer made of poly carbonate plastic.
Engraved with series of bumps.
Apply reflective aluminium coating.
1% more plastic.
Stick label.

Use of CD in computer:
Optical compact disc contains data.

CD burner:
Used to write data on CD.

CD ROM database:
Store computer data in the form of text and graphics.

CD ROM drive:
Optical disc contains audio or software data whose memory is read only.

How long does it take to burn CD:

700 MB of data takes about 3 to 4 minutes.

Types of CDs:

CD logo	Type of CD
DIGITAL AUDIO	normal pressed CDs (CD-DA)
DIGITAL AUDIO Recordable	consumer audio or music CD-R
DIGITAL AUDIO ReWritable	consumer audio or music CD-RW
Recordable	computer CD-R (audio, music and other files)
ReWritable	computer CD-RW (audio, music and other files)

Compact disc digital audio:
Reads audio tracks on CD.

Compact disc digital audio recordable:
Optical disc storage format.
Can be written once and read arbitrarily many times.

Arbitrary:
Based on random choice.

Compact disc digital audio rewritable:
Optical disc storage format.
Can be written, read arbitrarily many times, erased, and written again.

Compact disc recordable:
Holds 700MB of information.
Burn files on these disc only once.
Not reusable.

Compact disc rewritable:
Holds 700MB of information.
Burn files on them, erase them and reuse again.
Reusable.