How DVD works

I hope you had seen and enjoyed the previous posts about ipod & LCD TV.
Today, i have come up with DVDs, While researching to creating this post i found some astonishing facts, i hope your are going to become surprise to know how a DVD stores its data and how those data are read / fetched  from it.

DVD

The storage capacity of a DVD, six times that of a traditional CD, has revolutionized the way digital

data is organized and stored in the decade since its appearance in 1997. The DVD explosion

resounded in the world of home movies thanks to its capability of storing entire feature films,

bonus material, and subtitles (in various languages) on only one disc. The evolution of technology,

however, has not stopped with DVDs. Recent years have seen the introduction of discs able to hold 12

times the data of the DVD

Reading with Light

Optical discs (CDs and DVDs) are read by a

laser beam to obtain information. This

information is transformed into a binary electric

signal that is later interpreted and converted into

sounds, images, and data.

click on the images to enlarge

1.Laser emitter

generates a laser beam of

a specific wavelength.

2.Mirrors

guide the ray by working in

coordination.

3.  Direction

In order to read the disc,

the laser beam must strike

the surface of the disc

perpendicularly.

4. Lens

focuses the laser beam

before it reaches the surface

of the disc.

5. Reading

The laser beam strikes the

disc's reflective surface. The

reflection varies according

to the pattern of pits on the

disc's surface.

6. Prism

changes the direction of the

laser beam that reflects from

the disc and contains the

data read from the disc.

7. Photodiodes

translate the variations in the

returning laser beam and

convert them into a digital

signal.

Blue  light

Because blue light has a shorter wavelength than

red light (which is used in CDs and DVDs), a blue

laser makes it possible to read smaller pits, which

accounts for Blu-ray's greater storage capacity.

From the CD to Blu-ray
This comparison traces the evolution of the compact disc—especially its storage capacity.

CD

DVD

HDDVD

BR-DVD

Maximum capacity (single layer)	875MB	4.7 GB	15 GB	27 GB
Maximum capacity (double layer)	--	8.5 GB	30 GB	54 GB
Laser wavelength	789 nm	650 nm	405 nm	405 nm
Transfer rate in megabits per second (Mbps)	6	11.1/10.1	36.55	36/54
Resistance to scratches and dirt	No	No	No	Yes
Maximum video resolution	--	576 pixels	1,080 pixels	1,080 pixels
Supported formats	-- VCD and SVCD	DVD, VCD, SVCD, MPEG-2	MPEG-2, VC-1 (based on WMV), H.264/MPEG-4 AVC	MPEG-2, VC-1, MPEG-4 AVC

From the CD to Blu-ray, information storage has become

denser, and the wavelength of the reading beams has

become shorter.

1 millimeter = 1,000 micrometers (m)

1 micrometer = 1,000 nanometers (nm)