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.
Although many industry analysts predict that Blu-ray will replace DVDs in the next few years, there are quite a few barriers to the format's eventual adoption. First, there are other competing formats in the works such as HD-DVD, HD-DVD-9, and FVD which are all based upon existing DVD technology. The simple fact that DVD technology is already ten years in the market will help to significantly lower the cost of these competing systems, and compatibility with current DVDs means that one not replace his entire media library when upgrading hardware. Additionally, the perceived benefits of Blu-ray over DVD are of interest to only a very small segment of media consumers, as the video quality enabled by the high capacity discs is imperceivable on all but the largest HDTV sets. Lastly, consumers may be wary about changing disc formats less than ten years after the expensive switch to DVD.
Hardware Technology Terminology Questions