The DVD Format War
There's a lot of confusion about current DVD recording formats as well as what the next-generation DVD format will be. Understanding what's going on will make it easier for you to decide which system to use today as well as what to look forward to in the future.
The DVD has replaced the VCR as the mainstay of the home theater, a device which is rapidly in the process of joining the 8-track tape deck and the Polyester leisure suit in the garages, attics, and basements of history. Originally, there were two different formats proposed for the traditional DVD, but the hue and cry from the press and public brought the industry to its senses and a compromise was made creating a single DVD standard.
Unfortunately, the lessons taught from the VHS vs. Betamax wars didn't penetrate very far. Three different types of recordable DVD exist, and there is a storm brewing over the choice of the next-generation DVD format, a fight that has also broken down into two groups, each supporting their own system. It is almost certain that both formats will wind up on the shelves eventually.
Important note: This article does not deal with the intentional built-in incompatibility issue of regional DVD codes. The reason that the DVD you bought here and sent to your friend in another country doesn't work in their player is because the system was set up to prevent people from shipping discs from one market to another (all complaints should be sent to the MPAA.)
How DVD works
Since a laser can create as well as detect holes, it makes for an excellent way to store binary data. Binary math uses only the numbers zero and one. This can also be thought of as off-or-on, yes-or-no, empty-or-full, or what have you. On a DVD surface, the transition from light to dark (the start of the hole) is "1", and the transition from dark to light (the end of the hole) as "0", for example, to generate strings of numbers.
These numbers form the digital language that describes the data on the disc, be it music, movies, digital photographs, or computer data. The laser follows a regular track on the DVD like a needle follows the groove on a record, with the ability to both write and read information.
Recordable DVD formats
If you are making DVDs of your favorite TV shows so you can watch them with your Grandmother (fair use under copyright law), or are sending DVD copies of your home movies to family and friends, then your major concern is with the age of the machine they have. Older DVD players have a problem with recordable DVDs in general as the discs are not as reflective as pre-recorded DVDs, giving older machines that were not designed with the new formats in mind a harder time of it.
There are three main camps in the recordable DVD industry, and the two consumer-oriented systems have both a write-once and a re-writable version, each able to carry 4.7 gigabytes of data. Here is a breakdown:
DVD-R and DVD-RW: These are the write-once (DVD-R) and rewritable (DVD-RW) discs from what is referred to as the "Dash-R" group. ("Dash", not "minus".) The technology uses chemistry similar to that of CD-R, and once created, is playable in most new DVD players. DVD-R and DVD-RW discs must be prepared for playback in regular DVD players in a process called "finalizing", which adds the proper header tags and file info so that a player can "see" the information recorded on the disc.
DVD+R and DVD+RW: These are also write-once (DVD+R) and rewritable (DVD+RW) discs, but they come from the "Plus-R" group. DVD+R discs use a dye technology similar to that of DVD-R, and can also be played back in most players. DVD+RW discs are based upon CD-RW technology, and have the same playback problems on older machines that DVD-RW does. These discs must also be "finalized" before they can be played in another machine.
DVD-RAM: Just stay away from this one completely, unless you are looking for a computer-oriented backup format, which is what this type of DVD was designed for. It has clocking, defect-management, and rapid-access features useful for data applications, but these features also make it incompatible with most non-computer DVD players. Again, the important thing to remember is that there is no significant performance difference between the two major consumer formats of "Dash" and "Plus". Both formats will play back in most DVD players, so you can burn a disc and send it to someone for playback without a worry. The biggest problem you will have with recordable DVD is remembering whether you need "Dash" or "Plus" blank discs when you are standing in front of the shelf in the store about to buy some, as you can only use the blank media designed for each format.
Next-Generation DVD Sadly, the format wars aren't going to end anytime soon, although more and more multi-format DVD players are becoming available. There is also a brouhaha brewing over the technology that will replace DVD in the next few years. The important thing to remember here is that whatever system comes out on top, it will be able to play your current DVD collection (go ahead and exhale, your movie library is safe.)
The two new formats both use new blue-laser technology (even though only one format has it in its name), but the difference lies in the degree that the different formats use it. A blue laser emits a shorter wavelength of light than the red laser currently used, so the pits in the disc can be made smaller and placed closer together, resulting in a significantly higher data density.
How they differ:
HD-DVD uses a blue laser, but relies more on data compression than Blu-ray. The pits on an HD-DVD are smaller and closer together than on a current DVD, but not so small that you can't use current DVD manufacturing technology to make them, which is why the format is popular among some members of the industry. However, this transition ease for the manufacturer comes at a reduction in capacity - an HD DVD can "only" hold 15 gigabytes on a single-layer disc.
The fact is that the biggest reason HD-DVD has a following is because it is cheaper for a company to adopt. This is also the reason that VHS beat out Betamax, by the way. JVC (the inventor of VHS) almost gave away VHS licenses while Sony wanted a hefty fee, so everyone jumped on the VHS bandwagon.
The industry has made some attempts to compromise on a single next-generation DVD format, but to date the efforts have been fruitless.
Again, the important thing to remember is that whichever system you buy (they will almost certainly be sold side-by-side when they become commercially available), the new system will play your "old" DVDs. The biggest advantage to next-generation DVD will be in the amount of video that you can put on them, not the improvement in image quality (although there will be some) over what is currently available on DVD.