Lenovo ThinkPad 770 DVD Information Brief - Page 2

laser with a wavelength of 635 and 650 nanometers, designed to read through the thinner .6mm transparent layer. This makes it possible to focus on smaller pits of digital data, about half the physical size of pits on a CD-ROM -effectively doubling the density of pits on a DVD-ROM. More data is squeezed onto the disc by recording tracks closer together and closer to the center hole, as well as improving the error-correcting decoding algorithms. The result is a single-sided DVD that holds seven times as much data as a CD-ROM. The transfer rate is >2000KB per second, or roughly equivalent to a 14X-speed CD-ROM. This improved capacity and performance make it ideal for video-intensive multimedia applications. But that's just the most basic configuration . . . DVD discs come in capacities of 4.7, 8.5, 9.4 and 17GB. Most of the early discs will be singlesided, but the specification includes dual-layered and double-side versions that define the four levels of storage capacity. DVD data is read by a variable-focus laser; on dual-layered discs, a lens shifts the beam's focus from the pits on the outer layer to the pits on the inner layer. Capacity 4.7 GB 8.5 GB 9.4 GB 17 GB Layers 1 2 1 2 Sides 1 1 2 2 Movies provide an illuminating example of the huge capacity of DVD (1 DVD disc can hold the equivalent of 3264 high-density floppy disks) that makes it a natural as the universal storage format. A typical feature-length movie (133 minutes) will fit compressed on a single-sided disc. Gone with the Wind, which runs 220 minutes, will require two single-sided discs or a doublesided disc. Notice that a dual-layer disc doesn't have twice the storage capacity as a single layer disc; sandwiching two data layers (the top layer is semi-transparent) on the same side results in a degree of loss in reflectivity, critical to the optical pickup process. As a result, single and doublesided discs should be more common than the dual-layered variety. Eraser and Twister are among the first movie releases on double-sided discs, with a standard viewing ratio of 4:3 on one side, and the 16:9 letterboxed version on the flip side. Meet the DVD Family DVD-ROM (Read only memory) IBM is among the first to offer DVD-ROM drives, initially on the Aptiva C3D computer. Current industry trends indicate that on desktop models, MPEG-2 decoding will be implemented first on a PCI card, eventually migrating to the motherboard. Watching movies on your computer is just one application of DVD technology. Consider having a phone directory of virtually every business in the US at your fingertips, all on one DVD-ROM. That much data would fill six CDROMs. Multimedia titles are already available on DVD with 16-bit color instead of 8-bit, enhanced by full-screen MPEG-1 movies instead of quarter-frame QuickTime windows. DVD technology appeared first in the consumer market, with models that play (decompress) DVD movie titles using an advanced MPEG-2 video board (see "Compressing Digital Video," below). Several manufacturers introduced DVD players in March, 1997, opening the floodgate of competition that is already driving prices down from the $1,000 level of current top-of-the-line September 1997 2