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The CD ROM was introduced in 1982,The storage capacity of a CD is almost 650MB.CD’s are of different type ROM,R,RW.
The disc is of 1.2mm thickness & 120mm diameter .it consists of polycarbonate substrates, a reflective layer ,a data storage layer.
The data is stored as 1’s& 0’s,In conventional CDs, these 1s and 0s are represented by millions of pits s and land.
The discs are read using red lasers( 780nm wavelenth)
Data is encoded in the CD's in acontinuous spiraltrack, from the inside to the outside, about 1.6 to 2.2microns wide (a micron is 1/1000 of a millimeter)
technology : read
The pits and smooth areas (the smooth areas are called lands) are read by a laser when the disc is played.
Pits and lands reflect the light from the laser differently,
and that difference is encoded as binary data: the light hitting a land reflects back directly to a photodiode, whichgenerates an electrical pulse, while the light hitting a pit is refracted (deflected from a straight path, or scattered),and, consequently, reduced below the level needed to activate the photodiode.
a layer of organic polymer dye between the polycarbonate and metal layers serves as the recording medium.
Thecomposition of the dye is permanently transformed by exposure to a specific frequency of light.
While in the rotation by making the laser ON or OFF the the data is writing.
DVD is a relatively new optical disc technology that uses denser recording techniques
The original DVD format was launched in Japan in 1996.
A DVD is very similar to a CD, but it has a much larger data capacity. A standard DVD holds about seven times more data than a CD does(4.7GB).
The original purpose of DVD was to hold video data in particular - DVD once was said to stand for Digital Video Disk. However, as the number of DVD applications grew, the variety of data stored on DVD
The wave length of the laser beam used to read the DVD disc is shorter than that used for standard CDs
There are more tracks per disc on DVDs, because they are placed closer together than on CDs. The track pitch has been reduced to 0.74 microns.
Data pits are considerably smaller, which allows a greater number per track than on CDs.
HD DVD(High Definition DVD)
The HD-DVD format, developed and proposed by Toshiba & NEC was introduced to the DVD Forum in November of 2003 and approved as the next-generation DVD format.
It was developed to store highdefintion videos to get its full effect for HDTV.
This is the only high definition format which is approved
by the DVD forum
In HDDVD we are using Blue Violet laser (405nm) thus reducing the track pitch to 0.4 microns, Which increases the data capacity. The size of the pits is also reduced.
It holds a data rate of maximum 36.55 Mbps.
Blue Violet Laser
Shuji Nakamura, a Japanese researcher working in a small chemical company, Nichia Chemical Industries, built the first blue laser diode.
This uses the GaN(gallium nitride) , in the earlier time blue lasers were large and expensive gas laser instruments and needed high currents and strong cooling.
The disc of diameter 12cm & thickness 1.2mm
The disc contains polycarbonate subtrate layer in both sides .
There’s one reflective layer made of alumnium.
& a protective layer of lacquer
The recording layer is of organic dye, is highly sensitive to blue laser light, has the uncompromised readout stability essential for practical use.
Types of HDDVD
Single Layer HDDVD(15GB) Dual Layer HDDVD(30GB) Triple Layer HDDVD(45GB)
Dual layer HDDVD
DVD media has two dye layers for data recording. Each dye layer is separated by a spacer and a metal reflector.
The first reflector (positioned after the first dye layer) is semi-transparent; when the laser is focused a certain way, it will pass through this reflector and continue through to the second dye layer and can read the data
in the second dye layer.
The second reflector is completely opaque and will not allow the laser beam to pass any further
opportunity High Definition Media. Mass storage disc.
Appetite For HD Content Increasing Gap between “US HDTV households” (US HHs) and current cable/satellite offerings is great market opportunity HDTV US HHs 40 30 HD Dig Cable HD Satellite US HHs (MMs) 20 10 0 2003 2004 2005 2006 2007 2008 2009 2010 Source: Forrester Research – HDTV & the Coming Bandwidth Crunch, 2/17/2005
HDDVD in high definition media
HDDVD helps to view the high definition movies in its full effect.
It supports all the high definition formats such as MPEG-2,VC-1,MPEG-4,AVC.MPEG-2
needs 19.3Mbps. It can give up to data rate 36.55Mbps.
It supports video formats up to 1080i,1080p.
&HDTV video resolution 1920-1080.
High definition images offer a considerably richer colour palette with greater subtlety of colour transition and enhanced contrast. The result is greater precision, incredible detail and breathtaking realism.
Cheaper to produce in the short term when compare to blueray.
The only high definition format approved by the DVD forum.
The name itself, HD-DVD, is more consumer-friendly
HD-DVDs carry the same basic structure as current DVDs, so converting existing DVD manufacturing lines into HD-DVD lines is supposedly simple.
Backed by Microsoft.
disadvantages HD-DVD simply can't boast the same storage capacity as Blu-ray. HDDVD did not have the Hard coating .
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Thank you Shashwat Shriparv email@example.com InfinitySoft