The mechanism behind all optical disc players like Blu-ray and DVD is more or less similar. They use laser technology to read and write information on the discs. This is how digital information is stored on the discs:
- Optical discs have spiral paths (also known as tracks) that start from the centre of the disc and end at the edge of the discs.
- Very tiny pits on the tracks contain digital information which is encoded and decoded by the disc player unit.
- Smaller the pit size and closer the tracks, the more storage a disc will have.
When it comes to functionalities, a Blu-ray disc player differs a lot from a DVD player
- Blu-ray disc player uses blue laser to read and write data while DVD player uses red laser. As blue laser has shorter wave length of 405 nm (when compared with red laser of 650 nm wavelength), a blu-ray disc player can record much more information (ten times more than DVD player). Blue laser can be focused on smaller pits precisely so data can be read and processed much faster.
- The optical unit in blu-ray disc player uses improved optical features like powerful lens that can increase its aperture to 0.85 with ease.
- Thirdly, the pit size on a blu-ray disc is less than half of the pit size on a DVD (0.15 microns Vs 0.4 microns). The track length is also minimized on a blu-ray disc (0.32 micros) when compared with DVD disc (0.74 microns).
- Next, the polycarbonate layer over the bumps (which contain data) on the blu-ray disc is thinner (1.1 mm thickness) and this helps to remove optical aberrations and focus the laser more precisely on a smaller spot.
Recording and reading data from Blu-ray discs
The laser head of blu-ray disc player slides over the disc surface to read the video and audio data encoded on the bumps. The blue laser gets refracted from bumps & pits and the magnitude of received laser varies depends up on the surface it struck. The compressed, encoded digital information is decompressed and decoded by the disc player.
There are different formats of blu-ray discs available for recording purpose. BD-ROM is read-only disc and all blu-ray disc movies are BD-ROM. BD-R disc is recordable but only once and can be used with PC. BD-RW discs can be used for multiple times and can be used with PC. For recording HDTV content, you will require BD-RE discs.
Compression standards
DVDs and Blu-ray discs use different codecs or compression methods to store more data and usually, audio and video information is stored using different codecs. Most blu-ray disc players are compatible with codecs used in DVDs in addition to their additional codec features. This makes your blu-ray disc player to play DVDs also.
Blu-ray disc players support video compression standards like MPEG-2, VC1 and H.264/AVC and audio codecs that include DTS, Dolby Digital Plus, DTS HD and Dolby TrueHD.
Drive speeds and Data transfer speeds
A blu-ray disc player with 1X drive speed has a data transfer rate of 4.5 Mbits/s which is minimum standard for blu-ray disc players. For movies playback, any disc player with drive speed between 1X and 2X will provide enough transfer rate for both video and audio information. However, for recording HDTV content, higher drive speeds like 6X or above (54 Mbits/s) are highly desired.
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