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Blu-Ray Discs

Blu-ray Disc (BD) is a next-generation optical disc format meant for storage of high-definition video

and high-density data. The Blu-ray standard was jointly developed by a group of leading consumer

electronics and PC companies called the Blu-ray Disc Association (BDA), led by Sony and Philips. Blu-

ray has information capacity per layer of 25 gigabytes.

Blu-ray gets its name from the shorter wavelength (405 nm) of a "blue" (technically blue-violet) laser

that allows it to store substantially more data than a DVD, which has the same physical dimensions but

uses a longer wavelength (650 nm) red laser.

BD-R (R = Recordable once)

A single-layer Blu-ray disc (BD) can fit 23.3, 25, or 27 GB; this is enough for approximately four hours

of high-definition video with audio. A dual-layer BD can fit 46.6, 50, or 54 GB, enough for

approximately eight hours of HD video. Capacities of 100 GB and 200 GB, using four and eight layers

respectively, are currently being researched; TDK has already announced a four-layer 100 GB disc.

BD-RE (RE = REwritable)

The BD-RE (rewritable) standard is available, along with the BD-R (recordable) and BD-ROM formats,

which became available in mid-2004, as part of version 2.0 of the Blu-ray specifications. BD-ROM pre-

recorded media are to be available by early 2006.

In addition to 12 cm discs, an 8 cm variation for use with camcorders is planned that will have a

capacity of 15 GB.

To ensure that the Blu-ray Disc format is easily extendable (future-proof) it also includes support for

multi-layer discs, which should allow the storage capacity to be increased to 100GB/200GB (25GB per

layer) in the future simply by adding more layers to the discs.

Blu-ray drives currently in production can transfer approximately 36 Mbit/s (54 Mbit/s for BD-ROM),

but 2x speed prototypes with a 72 Mbit/s transfer rate are in development. Rates of 8x or more are

planned for the future.

Because the Blu-ray standard places data so close to the surface of the disc, early discs were

susceptible to dust and scratches and had to be enclosed in plastic caddies for protection. The solution

to this problem arrived in January 2004 with the introduction of a clear polymer that gives Blu-ray

discs unprecedented scratch resistance. The coating, developed by TDK Corporation under the name

"Durabis," allows BDs to be cleaned safely with only a tissue - a procedure that can damage CDs,

DVDs. Bare BDs with the coating are reportedly able to withstand attack by a screwdriver.

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