Blue Ray

The name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red, 650 nm laser. A single layer Blu-ray Disc can store 25 gigabytes (GB), over five times the size of a single layer DVD at 4.7 GB. A dual layer Blu-ray Disc can store 50 GB, almost 6 times the size of a dual layer DVD at 8.5 GB.

Blu-ray Disc is similar to PDD, another optical disc format developed by Sony (which has been available since 2004) but offering higher data transfer speeds. PDD was not intended for home video use and was aimed at business data archiving and backup.

Blu-Ray is currently in a format war with rival format HD DVD.

[edit] Technical specifications

* About 9 hours of high-definition (HD) video can be stored on a 50 GB disc.

* About 23 hours of standard-definition (SD) video can be stored on a 50 GB disc.

* On average, a single-layer disc can hold a High Definition feature of 135 minutes using MPEG-2, with additional room for 2 hours of bonus material in standard definition quality. A dual layer disc will extend this number up to 3 hours in HD quality and 9 hours of SD bonus material.

Physical size Single layer capacity Dual layer capacity

12 cm, single sided 25 GB 50 GB

12 cm, double sided 50 GB 100 GB

8 cm, single sided 7.8 GB 15.6 GB

8 cm, double sided 15.6 GB 31.2 GB

[edit] Laser and optics

The Blu-ray Disc system uses a blue-violet laser operating at a wavelength of 405 nm, similar to the one used for HD DVD, to read and write data. Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nm respectively.

[edit] Profiles

The BD-ROM specification defines four profiles of Blu-ray players. All video-based profiles are required to have a full implementation of BD-J.

[edit] 1.0

This is the basic profile that all current Blu-ray players (as of April 2007) are based on. Players based on this profile are only required to have 64 KB of application data area storage, which is typically used for bookmarks and other preference storage.[citation needed] Most players have more than the minimum required 64 KB.[citation needed] After October 31, 2007, this profile will be superseded by profile 1.1 as the new minimum profile.

[edit] 1.1 (mandatory November 2007)

What is typically referred to as "Profile 1.1" (but is more formally known as "Final Standard Profile") adds a secondary video decoder (typically used for picture in picture), secondary audio (typically used for interactive audio and commentary) and capability of supporting a minimum of 256 MB of local storage (for storing audio/video and title updates). Compliance with this profile will be mandatory for player models introduced to the market after October 31, 2007,[1] but existing products will be unaffected. As of July 24, 2007, only the Denon DVD-3800BDCI and DVD-2500BTCI have been announced as supporting this feature.[2]

Some profile 1.0 players may be upgradeable via firmware update to profile 1.1 if they have the appropriate hardware, but no manufacturer has announced any such upgrade. When software authored with interactive features dependent on Profile 1.1 hardware capabilities are played on profile 1.0 players some features may not be available or may offer limited capability. Profile 1.0 players will still be able to play the main feature of the disc, however.

[edit] 2.0 (BD-Live)

Profile 2, also known as BD-Live, adds network connectivity to the list of mandatory functions and increases mandatory local storage capability to 1 GB. No players have been announced as compatible with this profile. Players of earlier profiles will still be able to play the main feature of the disc, however.

[edit] 3 (audio only)

Profile 3 is meant for an audio-only player and does not require video decoding or BD-J.

[edit] Hard-coating technology

Because the Blu-ray Disc standard places the data recording layer close to the surface of the disc, early discs were susceptible to contamination and scratches and had to be enclosed in plastic caddies for protection. The consortium worried that such an inconvenience would hurt Blu-ray Disc's market adoption. Blu-ray Discs now use a layer of protective material on the surface through which the data is read.

The recent introduction of a clear polymer coating has given Blu-ray Discs substantial scratch resistance. The coating is developed by TDK and is called "Durabis". It allows BDs to be cleaned safely with only a tissue. The coating is said to successfully resist "wire wool scrubbing" according to Samsung Optical technical manager Chas Kalsi.[citation needed] It is not clear, however, whether discs will use the Durabis coating as a standard or only in premium discs.

Both Sony and Panasonic replication methods include proprietary hard-coat technologies. Sony's rewritable media are sprayed with a scratch-resistant and antistatic coating. Verbatim recordable and rewritable Blu-ray Disc discs use their own proprietary hard-coat technology called ScratchGuard.

[edit] Ongoing development

Although the Blu-ray Disc specification has been finalized, engineers continue working to advance the technology. Quad-layer (100 GB) discs have been demonstrated on a drive with modified optics. Furthermore TDK announced in August 2006 that they have created a working experimental Blu-ray Disc capable of holding 200 GB of data on a single side, using six 33 GB data layers.[3] Such discs would probably not work on today's players, as these devices are only designed and tested on discs that meet the current specification.

Also behind closed doors at CES 2007, Ritek has revealed that they had successfully developed a High Definition optical disc process that extends the disc capacity of both competing formats to 10 layers. That increases the capacity of the discs