Blu-ray and DVD formats

BLU-RAY
Developed by Sony, Blu-ray Disc (BD) is a next-generation optical disc format meant for storage of high-definition video and high-density data. The Blu-ray standard was jointly developed by a group of consumer electronics and PC companies called the Blu-ray Disc Association (BDA). Compared to the HD DVD format, its main competitor, Blu-ray has more information cap...acity per layer, 25 instead of 15 gigabytes. Blu-ray gets its name from the shorter wavelength (405 nm) of a “blue” (technically blue- violet) laser that allows it to store substantially more data than a DVD, which has the same physical dimensions but uses a longer wavelength (650 nm) red laser.

Dvd>
DVD-R A DVD-Recordable or DVD-R is an optical disc with a larger storage capacity than a CD-R, typically 4.7 GB (4.38 GB) instead of 700 MB, although the capacity of the original standard was 3.95 GB. Pioneer developed the 8.54 GB dual layer version, launched in 2005. A DVD-R can be written to only once, whereas a DVD- RW (DVD-rewritable) can be rewritten multiple times. The DVD-R format was developed by Pioneer in autumn of 1997. It is supported by most DVD players, and is approved by the DVD Forum. DVD-R discs are composed of two 0.6 mm polycarbonate discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver, silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved “dummy” disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD’s 1.2 mm of polycarbonate, a DVD’s laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size, which is key for writing smaller pits. In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control etc.