ADVANTAGES OF BLU_RAY DISC:

· Record High-Definition Television (HDTV) without any quality loss.

· Instantly skip to any spot on the disc.

· Record one program while watching another on the disc

· Create play lists.

· Edit programs recorded on the disc.

· Automatically search for an empty space on the disc to avoid recording over a program.

· Access the web to down load subtitles and other extra features

WORKING OF BLU_RAY:

Discs store digitally encoded video and audio information in pits spiral grooves that run from the center of the disc to its edges. A laser reads the other side of these pits the bumps to play the movie or program that is stored on the DVD. The more data that is contained on a disc, the smaller and more closely packed the pits must be. The smaller the pita (and therefore the bumps), the more precise the reading laser must be.

Unlike current DVD’s, which use a red laser to read and write data, Blu-ray uses a blue laser (which is where the format gets its name). A blue laser has a shorter wavelength (405 nanometers) than a red laser (650 nano meters). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are not only 0.15 microns long this is more than twice as small as the pits on a DVD.Plus, Blue-ray has reduced the track pitch from 0.74 microns to 0.32 microns. The smaller pits, smaller beam and shorter track pitch together enable a single-layer Blu-ray disc to hold more than 25GB of information about five times the amount of information that can be stores on a DVD.

Each BIu-ray disc is about the same thickness (1.2 millimeters) as a DVD. But the two types of discs store data differently. In a DVD, the data is sandwiched between two polycarbonate layers, each O.6-mm thick. Having a polycarbonate layer on top of the data can cause a problem called birefringence, in which the substrate layer refracts the laser light into two separate beams. If the beam is split too widely, the disc cannot be read. Also, if the DVD surface is not exactly flat, and is therefore not exactly perpendicular to the beam, it can lead to a problem known as disc tilt, in which the laser beam is distorted. All of these issues lead to a very involved manufacturing process.

BUILDING OF BLU-RAY:

The BIu-ray disc overcomes DVD-reading issues by placing the data on top of a l.l-mmthick polycarbonate layer. Having the data on top prevents birefringence and therefore prevents readability problems. And, with the recording layer sitting closer to the objective lens of the reading mechanism, the problem of disc tilt is virtually eliminated. Because the data is closer to the surface, a hard coating is placed on the outside of the disc to protect it from scratches and fingerprints.

The design of the BIu-ray discs saves on manufacturing costs. Traditional DVDs are built by injection molding the two O.6-mm discs between which the recording layer is sandwiched. The process must be done very carefully to prevent birefringence.

1. The two discs are molded.

2. The recording layer is added to one of the discs.

3. The two discs are glued together.

BIu-ray discs only do the injection-molding process on a single I.I-mm disc, which reduces cost. hat savings balances out the cost of adding the protective layer, so the end price is no more than the price of a regular DVD.

BLU-RAY VS OTHER NEW DISC FORMATS:

Will Blu-ray replace previous DVDs? Its manufactures hope so. In the meantime JVC has developed a Blu-ray /DVD combo disc with an approximate 33.5GB capacity, allowing for the release of video in both formats on a single disc. But Blu-ray is not alone in the marketplace. A few other formats are competeting for a share of DVD market.

HD-DVD:

The other big player is HD_DVD, also called AOD(Advanced Optical Disc), which DVD and can therefore be manufactured with the same equipment, saving on costs. The disadvantage is that it can’t match the storage capacity of Blu-ray. A rewritable, single layer HD_DVD can hold 20 GB of data; a double –layer disc can hold 30 GB(that’s compared to 27 GB and 50 GB for Blu-ray). The read-only versions hold slightly less data. Also, HD_DVD doesn’t offer the interactive capabilities of Blu-ray , although it will probably be less expensive than its competitor

OTHER COMPETETORS:

Blu-ray and HD-DVD are the two major competitors in the market, there are other contenders, as well. Warner Bros. Pictures has developed its own system, called HD-DVD-9. This system uses a higher compression rate to put more information (about two hours of high –definition video) on a standard DVD. Taiwan has created the Forwarded Versatile Disc(FVD), an upgraded version of today’s DVDs that allows for more data storage capacity (5.4 GB on a single –sided disc and 9.8 GB on a double-sided disc). And China has introduced the Enhanced Video Disc (EVD), another high-defnition video disc

There are also professional versions of the Blu laser technology. Sony has developed XDCAM and ProData (Professional Disc for Data). The former is designed for use by broadcasters and AV studios. The latter is primarily for commercial data storage (for example ,backing up servers).