Deciphering the DVD maze.

DVD, an important platform for video, audio and data content storage, is very young and as such is still evolving. There are a myriad of ways to create and play DVDs, and the technology continues to make it more complex.

First, the basics: DVD stands for Digital Versatile Disc, DVD R for DVD Recordable and DVD RW for DVD ReWriteable. "Recordable" indicates that content can be added to the disc once, while in "ReWritable," content can be added and erased and added again.

A single side DVD (technically DVD-5) stores up to two hours of good quality DVD-Video, including several audio tracks in formats like stereo, Dolby Digital or DTS, as well as advanced menu systems, subtitles and still pictures that can be played by standalone DVD players and computer DVD-ROMs. The ROM parts of a DVD, or the Read-Only-Memory, can, however, only be played on a computer.

There are currently three competing DVD recording standards: DVD-R and -RW (the "minus" standard); DVD+R and +RW (the "plus" standard); and DVD-RAM (Random Access Memory, which reads and writes its own special discs). For explanations see below.

There are also various read/write modes used by these standards: CLV, CAV, P-CAV, and the most confusing of all, Z, which is sometimes referred to as Z-CAV and sometimes Z-CLV, which are, in effect, the same thing.

CLV stands for Constant Linear Velocity, and means that the disc is read/written at a constant speed. It is used in the "plus" and "minus" standards. CAV stands for Constant Angular Velocity, and means that the disc is read/written at a constantly increasing speed. It is used only in the "plus" standard. P-CAV, or Partial-Constant Angular Velocity, means that the disc is read/written at an increasing speed until it reaches a certain maximum speed. After this point, the disc is read/written at that maximum speed for the rest of the operation. Z-CLV/Z-CAV stands for Zone-Constant Linear (or Angular) Velocity. In this case, the disc is divided into zones and after each zone is written, the speed is increased. Note that this mode is not used when reading a disc.

Now onto the three recording standards: DVD-, DVD+ and DVD RAM. DVD-R and DVD-RW was the first DVD recording format compatible with standalone DVD players. It supports CLV, but not CAV. DVD-R/W can handle single side 4.7 GB DVDs and double side 9.4 GB DVDs (called DVD-10). DVD-R is compatible with about 88 percent of all DVD players and DVD-ROMs; DVD-RW is compatible with about 69 percent. DVD+R and DVD+RW has some better features than DVD-R/W, such as lossless linking and compatibility with both CAV and CLV, making it ideal for both data and video. Like DVD-R/W, DVD+R/W supports single side and double side DVDs. DVD+R is compatible with about 84 percent of all DVD players and DVD-ROMs; DVD+RW is compatible with about 70 percent. DVD-RAM has the best recording features of all, but is not compatible with most DVD-Video players and DVD-ROM drives. It uses the "Z" mode to record data and can be thought of as a removable hard drive.

If all this weren't enough, a new type of DVD recorder is going to be introduced this fall that may make all previous versions obsolete. The new recorders will use a "Blu-ray" laser (as opposed to the red lasers used today) and will be able to store up to 27 GB of data on a single disc--enough room to record high-definition TV.