Blu-Ray is an optical disc format, similar to CD and DVD. Blu-Ray's main advantage over CD and DVD formats is the 25 GB capacity
of a single-layer single-sided Blu-Ray disc: over five times that of a comparable DVD, and over 35 times that of a comparable CD.
Additionally, Blu-Ray specifications call for a threefold increase in read speed over current DVD offerings. This leads to higher
definition video and audio, of especial importance in HDTV applications.
Multi-layering technology has been adapted to double the capacity of Blu-Ray discs in standard consumer applications, and experimental
versions have be displayed with up to a tenfold increase
in storage space. Additional benefits of Blu-Ray players over DVD players include Internet connectivity for downloading subtitles and
updated features, a built-in Java virtual machine bringing interactivity to a new level, and writable areas of the disc for saving
preferences such as subtitle fonts, bookmarks, and usage statistics.
The name Blu-Ray is a reference to the technology that makes the high capacity discs possible. Conventional CD players read the disc with a
780 nanometer laser, just bordering on infrared. This requires a 1.6 micrometer track pitch, which is actually visible to the naked eye. As
technology progressed, DVDs were introduced with 650 nanometer wavelength, which is perceived by the human eye as a light red. The shorter
wavelength required less than half the track pitch of CDs, at 0.74 micrometers.
The combined effect of the smaller data pits made possible by
the short-wavelength laser and the thinner track pitch is responsible for the DVD's relatively high data capacity. In comparison, Blu-Ray discs
use an ultra-short 405 nanometer wavelength laser, which the human eye perceives as a deep blue or purple. The short wavelength requires only
0.3 micrometers of track pitch, less than a third of a DVD's track pitch and less than a fifth of a CDs track pitch. This allows the data pits
to be super-small and very densely packed onto the disc's surface. Hence, disc capacity is increased.
