There are two types of combination HD DVD/Standard DVD discs on the market today. One, simply called the “combo disc,” has two sides: one for play in an HD player, the other for use in a standard DVD player. The other, called the “twin format,” is one-sided, but has two layers of data encryption—one for HD and one for the standard player.
The combo DVD is two-sided. A red laser reads the standard side, and a blue laser reads the HD side. Each is completely compatible with both standard and HD players, but you’ll have to remember to flip the disc over.
The combo DVD has seen market support in the past: Universal announced at the end of 2006 that 90% of its movie titles for 2007 would be released on combo DVD’s. Later in the year, however, Universal announced that it was scaling back its support of the combo format, possibly because of the added cost of laying two sides of content to each disc.
The Twin DVD has two layers of digital content on one side. The standard content is read by a red laser, and the HD content is read by a blue laser. Each content format is invisible to the other; the blue laser can’t read the standard track, and vice versa.
The twin was originally released with two layers, but the newer twin discs have three layers. This allows for some flexibility: one layer of standard video, plus a dual layer of HD video, making giving the HD version of the disc essentially the same storage space as a DL disc, or a dual standard layer.
There are also combo Blu-Ray/Standard discs on the market that perform the same function. All of these are a great way to introduce consumers to the new technology. They allow consumers to upgrade when they want, without replacing all their discs. Hopefully, they’ll remain on the market long enough to catch on.