Up to Speed on DVD.(DVDs in library collections)

IT COULD - AND SHOULD - BE YOUR LIBRARY'S NEXT MEDIUM

Who needs a new medium? Books form the basis, you have CDs under control, and VHS videos work well enough. Anyway, won't everything arrive on the Internet any day now? If you're a true believer in that last statement, go on to the next article. For the rest of us, it's a good time to get up to speed on DVD.

What DVD stands for depends on whom you ask. During the development effort, it stood for Digital Video Disc or Digital Versatile Disc, but now it just stands for DVD. It is not going to replace any other medium overnight, but DVD is already widely used and has all the earmarks of a long-term success. Statistics on the number of libraries that currently are using DVDs have not yet been collected because the medium is still so new, according to Mary Jo Lynch, director of ALA's Office for Research and Statistics. But it's not too early to think about it - and this is a medium that libraries should love.

What it is

Most DVDs look exactly like CDs: 12 cm diameter, aluminum-color with rainbow diffraction on one side, label on the other. They're even the same thickness as CDs: Physically, the two are indistinguishable. That's not always quite true - if you pick up Austin Powers: International Man of Mystery or quite a few other DVDs, you'll find that there's no label side - both sides look the same.

A DVD is a "fancy CD" - a laser-read stamped disc containing billions of tiny pits and lands in one very long track. The DVD laser has a shorter wavelength, and the pits and lands are shorter and narrower, which means that the DVD's track can contain 4.7 billion bytes of raw data (4.7 GB), seven times the capacity of a CD.

There's a little more to it than that, and Austin Powers tips off one aspect. A DVD is essentially two half-thickness CDs laminated together - although many DVDs (those with full label sides) use blanks for the second side. A two-sided DVD can carry twice as much data (up to 9.4 GB), although you have to flip it over to play both sides.

Additionally, each side of a DVD can have two information layers, one of them semitransparent. The second layer can't hold quite as much data as a single layer, but it's still possible for a one-sided dual-layer DVD (the …