DVD Region 1 - The Weather Underground - Video & DVD

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1. A single-layer DVD can store 4.7 Gbyte, which is around seven times as much a standard CD-ROM. By employing a red laser at 650 nm (was 780 nm) wavelength and a numerical aperture of 0.6 (was 0.45), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which has the same characteristics as classic EFM. The CD subcode is removed. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a "third" error correction layer.

2. A 74-minute (650MB) disc has roughly 333,000 sectors while the 80 minute (700MB) one has approximately 360,000 sectors allowing greater storage. 90 and 99 minute versions follow the same logical extension cramming more sectors at the cost of reliability across drives. Pits are much closer to the label side of a disc, so that defects and dirt on the clear side can be out of focus during playback. Consequently, discs are much easier to ruin by scratching their label side, whereas clear-side scratches can be repaired by refilling them with plastic of similar index of refraction.