How does a DVD work?

Extremely Dense with Much Capacity

DVD, popularly know as the Digital Versatile Disc (it really means Digital Versatile Disc), is the next generation of optical disc media.Though a DVD looks like a CD, inside it holds between 7 and 25 times the data. That means a new level of quality and convenience for movies, music, multimedia and interactive software. Never before has one new technology changed so many aspects of home entertainment.

Minimum Seven Times the Data of a CD

DVD achieves its huge capacity by packing more data into the same physical space as a CD. It does this in several ways. First, it's tracks are closer together and the pits in each track are smaller. Second, new data compression technology is highly efficient, minimizing the need to store repetitive of unneeded data. Third, two separate layers of tracks can be combined into a single DVD disc. For movies, this adds up to a minimum of 2 hours and 13 minutes of video play. A dual-layer disc provides 4-hour play, and doesn't need to be turned over. A single layered double-sided disc provides about 4 hours and 30 minutes.Longer playing times are only the most obvious advantage. DVD's huge capacity also supports ultra-realistic picture quality and hi-fi sound not to mention interactive multimedia enhancements.

DVD 5 (4,7 GB) One coat, one-side scanning	DVD 9 (8,5 GB) Double coat, one-side scanning
DVD 10 (9,5 GB) One coat, two-side scanning	DVD 17 (17 GB) Double coat, two-side scanning

All the Advantages of an Optical Disc

Like a compact disc or laserdisc, DVD permits random access to any point on the disc. There's no need to shuttle forward or backward through a tape, and of course there's no rewinding. As an optical disc, DVD never physically contacts the pickup. The disc is played by a beam of laser light, so there is no wear and tear even if you keep replaying the same scene. The tough plastic surface is forgiving of fingerprints, dust and dirt. Care is the same as for compact discs - no special treatment needed. This means that you can play your DVD collection thousands of times and continue to enjoy the same beautiful picture and sound quality.

How is it Different from CD 's?

On the outside, a DVD is virtually indistinguishable form a CD. It has the same 5" diameter and 1.2mm thickness. Like a CD, it's easy to carry, safe to handle, and is just the right space-saving compact size for home entertainment. The only difference is the format and the amount of information.

Smaller Pits, Narrower Track Pitch Inside

Compact Disc           

DVD disc        

On the inside, a DVD is totally different. Its pits are half the size of CD pits (0.4µm vs. 0.83µm), and it's tracks are spaced about twice as closer together (0.74µm vs. 1.6µm). See following image...

Thin-Substrate Bonded Disc

In a CD player, the laser bean has to pass through a relatively thick layer of plastic to reach the data pits. To help a DVD player focus on its smaller pits, a DVD disc uses a thinner plastic substrate. By itself, such a thin disc would not stay flat or withstand handling. Therefore, every DVD is joined to a second 0.6mm substrate, using bonding technology developed by Panasonic. On a single-layer disc, one of the two substrates has no recorded data.

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