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What is Blu-ray?
Blu-ray Disc (BD), also known as Blu-ray is the name of a next-generation high-definition video (HD), optical disc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's leading consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson).
The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. A single-layer Blu-ray Disc can hold 25GB, which can be used to record over 2 hours of HDTV or more than 13 hours of standard-definition TV. There are also dual-layer versions of the discs that can hold 50GB.
The name "Blu-ray" comes from the fact that this new format uses a blue-violet laser while current optical disc technologies such as DVD, DVD±R, DVD±RW, and DVD-RAM use a red laser to read and write data. Despite the different type of lasers used, Blu-ray products can easily be made backwards compatible through the use of a BD/DVD/CD compatible optical pickup and allow playback of CDs and DVDs. While the red laser wavelength is 650nm, a blue-violet laser used in Blu-ray is (405nm). The benefit of having a shorter wavelength makes it possible to focus the laser spot with vastly improved accuracy. This allows data to be packed more tightly and stored in less space, so it's possible to fit more data on the same sized disk. The ability to better focus the Blu-ray laser together with the ability to shrink the distance of the numerical aperture that holds the data to 0.85 is what enables Blu-ray Discs to hold 25GB/50GB.
With the breakneck growth of HDTV because of consumer demand the demand for the ability to record HD programming is quickly rising. Blu-ray was designed with this application in mind and according to the developers of the Blu-ray standard when it launches it will have supports direct recording of the MPEG-2 TS (Transport Stream) used by digital broadcasters. This means that HDTV broadcasts can be recorded directly to the disc without any quality loss or extra processing. To handle the increased amount of data required for HD, Blu-ray employs a 36Mbps data transfer rate. In addition, by fully utilizing an optical disc's random accessing features, it's possible to playback video on a disc while simultaneously recording HD video.
DVD
Blu-ray
Disc type
DVD-ROM
(Read-Only)Blu-ray
(Read-Only)Disc diameter
120mm
120mm
Disc structure
0.6mm
x 2 substrates0.85mm
x 2 substratesCapacity
(Single-sided,
single-layer)
(Single-sided,
dual-layer)4.7GB
8.5GB25GB
50GBPlayback time*
Recording time*4.7GB, SD resolution:
132minutes
8.5GB, SD resolution:
238minutes25GB, HD resolution:
over 6+ hours
50GB, HD resolution:
over 13 hoursLaser Wavelength
650nm
(red laser)405nm
(blue laser)Compression
technologyMPEG-2
MPEG-4 AVC/
VC-1/MPEG-2User bit rate
11.08Mbps
36.55Mbps
According to supporters and developers of Blu-ray they believe it will replace VCRs and DVD recorders as consumers make the transition to HDTV over the coming years.
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