What's a Blu-Ray Disc? - dummies

By Danny Briere, Pat Hurley

Blu-ray discs, developed by Sony Corporation, are the high-definition media storage alternative to DVDs. Blu-ray gets its name from the color of the laser that reads the discs inside a Blu-ray player; traditional CDs and regular DVDs use a red laser. The blue laser has a smaller wavelength and is more suited to reading the physically smaller spots on the disc itself. This ability to focus in on smaller spots allows the disc to have more spots — and more spots means more data.

Here are some details on Blu-ray discs:

  • Blu-ray discs can hold up to 50GB of data (more than five or six times what a standard DVD can hold). That 50GB capacity is for a dual-layer disc; a single-layer disc can hold 25GB of data — enough space for at least two hours of high-definition programming. Storage space is the key for high-definition disc formats simply because HDTV takes up as much as nine or ten times the storage space than does a standard-definition DVD-quality video.

    Blu-ray discs can hold even more data if the disc is encoded using a more efficient codec (such as MPEG-4 instead of MPEG-2), which means you can potentially fit four hours of high definition video on a single-layer disc.

  • Blu-ray discs support the same audio formats that a regular DVD supports, but also include the Dolby Digital Plus and Dolby TrueHD formats. Because few A/V receivers include decoders for these new formats today, Blu-ray disc players have a built-in surround-sound decoder that lets you use these higher-resolution audio formats.

Because the physical structure of a Blu-ray disc is even more susceptible to scratching than DVD, the Blu-ray folks decided up front to include a hard coating on each Blu-ray disc. Advanced polymers cover the surface of a Blu-ray disc, so go ahead and let your 2-year-old carry the disc to and from the player — she won’t make her favorite scene unwatchable due to scratches.