How Blu-ray Discs Work

Page content


First came CDs with 500 MB of capacity. Then the DVD made a quantum jump to 4.7 GB. In some circumstances, the capacity could be cranked up to 17 GB! That is a lot of entertainment in one handy, convenient package. But soon the improvements in TV were pushing the frontiers again. High definition TV used a lot more resolution compared to standard TV. That started a a scramble to discover a new media so that the whole content would still be handy and convenient on one disc.

There was a format war of how the content would be recorded. Blu-ray is the winner since the rival camp HD-DVD led by Toshiba gave up. While the DVD was a consensus development without getting into product wars, the Blue-ray and the HD-DVD war continued for some time and delayed stability in the market for consumers.

Blu-ray operation

For a detailed look at the media and recording/ reproducing technology look up the Blu-ray association site They have general explanations, and technical details in greater depth. Unlike the DVD, developed by consensus, Shuji Nakamura is credited with the inventor of the first practical blue-violet laser that made the discs possible. The association has 19 board members which include computer heavy weights like Apple, Dell, Sun, Samsung, Sony and studio heavyweights like 20th Century Fox, Disney and Warner Brothers.

The Blu-ray discs also operate the same way CDs and DVDs operate. The exact same physical form factor allows for easy backward compatibility. The real difference is it uses a blue-violet laser that has a much smaller wavelength than the red laser used in DVDs. Compared to a DVD track pitch of 0.74 micron, the Blu-ray uses a track pitch of 0.32 micron. While the maximum pit length on a DVD was 0.4 micrometer; the maximum pit length on a Blu-ray is 0.15 micrometer. That directly affects its success in recording and reading more data on the surface of the discs. Use of better lenses help focus the laser on to the disc surface more sharply too and that helps. So much so that, compared to the maximum of 17 GB of data ( 9.4 being more common) of a DVD disc, a dual layer, double sided Blu-ray disc can accommodate up to 50 GB! That will hold a complete HD Movie and bonus material. Besides, this is a useful size for data backup uses too.

So the blue-violet laser bouncing off the disc surface has the capacity of reading/ writing more data in the same space as the pits representing the presence or absence of data are much smaller. Recording is made in the same spiral fashion on multiple tracks. Data read-off is then passed onto the electronic part of the player to decompress the data, convert to analog and take care of de-scrambling and the region code too. While discs initially needed a cartridge to protect them from scratches, a hard coating developed later provides enough protection. Cartridges are not used anymore.

Content Protection and Region Code

An advanced content protection scheme has been developed for Blu-ray disks to reassure content providers that this can prevent piracy. It is actually a better solution that the CSS. While the implementation of CSS was voluntary, it is mandatory for Blu-ray players. There are three region codes. Region A includes countries in North, Central and South America, Korea, Japan and SE Asia. Region B includes countries in EMEA, Australia and New Zealand. Region C has countries like India, China, Russia and the rest of the world.

Writeable media

Like DVD options, there are similar choices in the disc media available which let you write and re-write on some of these discs. So adding content to an existing disc, or erasing and completely rewriting a disc is no problem. Whether as data back up/restore or changing / updating your personal media library there are no problems at all. These are called the BD-RE media.

Blue-ray Usage

Combined with the random access ability of these discs, as with DVDs, the Blue-ray discs are ideal for applications like High Definition Television Recording, HD Video Distribution, HD Camcorder Archiving, Mass Data Storage, Digital Asset Management and Professional Storage.