Storage Amounts on Discs - Blue-Ray vs HD-DVD
- A current, single-sided, standard DVD can hold 4.7 GB ~ about the size of an average two-hour, standard-definition movie with a few extra features.
HD-DVD (or AOD, Advanced Optical Disc) developed by Toshiba & NEC.
- A rewritable, single-layer HD-DVD can hold 15 GB of data
- a double-layer disc can hold 30 GB
- a triple-layer disc can hold 45 GB
- A single-layered standard Blu-ray disc can hold 27 GB ~ more than 13 hours of standard-definition video or more than 2 hours of high-definition video.
- A double-layered Blu-ray disc can hold 54 GB ~ more than 20 hours of standard-definition video or more than 4.5 hours of high-definition video.
- JVC has developed a Blu-ray/HD-DVD combo disc with an approximate 33.5-GB capacity.
- Pioneer is developing an optical disc that uses ultraviolet, which has a shorter wavelength than blue lasers, with a storage capacity of an astounding 500 GB of data.
Blue Ray Formats
BD-ROM (read-only) - for pre-recorded content
BD-R (recordable) - for PC data storage
BD-RW (rewritable) - for PC data storage
BD-RE (rewritable) - for HDTV recording
Blu-ray also has a higher data transfer rate -- 36 Mbps (megabits per second) -- than today's DVDs, which transfer at 10 Mbps. A Blu-ray disc can record 25 GB of material in just over an hour and a half.
The design of the Blu-ray discs saves on manufacturing costs. Traditional DVDs are built by injection molding the two 0.6-mm discs between which the recording layer is sandwiched. The process must be done very carefully to prevent birefringence. Blu-ray discs only do the injection-molding process on a single 1.1-mm disc, which reduces cost. That savings balances out the cost of adding the protective layer, so the end price is no more than the price of a regular DVD. with the recording layer sitting closer to the objective lens of the reading mechanism, the problem of disc tilt is virtually eliminated therefore prevents readability problems.
All information collected from the site, How Stuff Works
