As the format name directly indicates, a newly developed blue laser diode has been adopted, providing a storage capacity of 25 GB on a single-layered disc or 50 GB on a dual-layered disc with a 12 cm diameter (same size as CD and DVD). The data transfer rate reaches 36 Mbps (bit per second).

Blu-ray discs not only have more storage capacity than traditional DVDs, but they also offer a new level of interactivity. Users will be able to connect to the Internet and instantly download subtitles and other interactive movie features. With Blu-ray, you can:

• 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 playlists
• Edit or reorder programs recorded on the disc
• Automatically search for an empty space on the disc to avoid recording over a program
• Access the Web to download subtitles and other extra features

Unlike current DVDs, 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 nanometers). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are only 0.15 microns (µm) (1 micron = 10-6 meters) long — this is more than twice as small as the pits on a DVD. Plus, Blu-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 25 GB of information — about five times the amount of information that can be stored on a DVD.

Blu-ray’s  modes of Operation:

• HDMV (High Definition Movie)
• BD-J (Blu-ray Disc Java)

Both massively surpass the DVD specification in use today.

HDMV mode

HDMV has been designed to support a feature set that supersedes DVD-Video while emphasizing production continuity with existing media formats. HDMV supports all of the well known DVD-Video features.

”Out-of-mux” reading:
While playing the movie the system can call up menus, overlay     graphics, pictures, button sounds, etc. at user request without stopping playback.

The HDMV decoder model is equipped with two read buffers, two preloading buffers and two switches.

When you start to play a movie the main MPEG stream is sent to the primary read buffer and the Out-of-Mux stream is sent to the secondary read buffer by the switch.
The preloading buffers cache subtitles, interactive graphics and sound effects data before movie playback begins and supplies data for presentation even while the main MPEG stream is being decoded.

BD-J
BD-J, or Blu-ray Disc Java, is the interactive platform supporting advanced content for Blu-ray Disc. BD-J mode was designed to offer the content provider almost unlimited functionality when creating interactive titles. It is based on Java 2 Micro Edition.

BD-J allows bonus content on BD titles to be far more sophisticated on DVD. Like network access, picture-in-picture and access to local storage.

Having a full programming environment available on every Blu-ray Disc player provides developers with an extremely flexible platform for creating innovative new content types.

Blu-ray vs HD-DVD

During the high definition optical disc format war, Blu-ray Disc competed with the HD DVD format
BD                 vs                 HD-DVD

Capacity:                50Gb                                  30Gb
AV transfer rate:    54Mbps                              36.55Mbps
Movie studios:        7/8                                    3/8
Blu-ray has bigger               HD-DVD is more
Hardware support                Cost effective (fall 2006).

On February 19, 2008, Toshiba — the main company supporting HD DVD — announced it would no longer develop, manufacture and market HD DVD players and recorders,leading almost all other HD DVD supporters to follow suit, effectively naming Blu-ray the victor of the format war.