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Double your pleasure

What's a dual-layer DVD? Are they worth the money?

Dual-layer DVDs record more information on a single DVD — 8.5 Gb versus 4.7 Gb on a single-layer disk. While that's handy, dual-layer DVDs are probably of most interest to gamers and media junkies. The reason is that the next generation of DVDs, using blue lasers and holding more than 27 Gb of information, will probably start appearing in a few months.

Unlike a double-sided DVD (a much rarer beast), a dual-layer DVD reads and writes both layers from the same side of the disk. The layers are at different depths in the disk's plastic coating and the drive's laser changes focus depending on which layer it is reading or writing.

The most immediate interest in dual-layer DVDs comes from companies that want to pack a lot of information onto a DVD right now. This includes media companies that like the idea of putting an entire movie and a whole pile of extras on a single disk and gaming companies with really, really big games. As a result, computer users buying dual-layer drives tend to be people who like to play games and use their computers to watch movies.

Dual-layer drives and disks are both new, so prices are somewhat higher than conventional single-layer disks and drives. But as with all technological toys, these devices get less expensive almost on a daily basis.

As noted, the next generation of digital disks is already on the horizon. They will use a blue laser and store 27 Gb in a single layer format. Blue laser DVDs are inherently rewritable and the first versions products will probably be available this year (2005). As a result, a lot of computer users are planning to bypass dual-layer DVDs in favor of one of the blue laser formats.

One caveat on video playback: when a dual-layer disk gets to the end of one layer and has to change to the other, there is often an ever-so-slight delay. This can be particularly irritating during a movie or a game. No, your computer and drive are not having problems — but it's the nature of the beast.