Isn't technology wonderful? Less than 25 years ago people were only able to watch movies at a cinema or at home using very expensive projectors. Today, the different formats for video are numerous, including VHS, laser-disc, video CD, and of course, DVD.

DVD stands for both 'digital video disc' and 'digital versatile disc'. The disc itself is a flat piece of shiny silver plastic almost five inches across which looks remarkably like a CD. The one thing it has in common with the CD format, apart from its size, is that you can easily scratch it, so instead of your movie collection being chewed up and ruined by your dodgy video player, you can only ruin it yourself.

How DVD is Different

The difference between DVD and most other consumer data storage formats, and the reason why it is such a popular new format, is the amount of information one single disc can contain. There are four common types of pre-recorded DVD-video disc, named by the approximate amount of data they hold.

• DVD-5 single sided, single layer - about 4.5 gigabytes
• DVD-9 single sided, double layer - about 8.5 gigabytes
• DVD-10 double sided, single layer - about 9.5 gigabytes
• DVD-18 double sided, double layer - about 17 gigabytes

Many double layer discs use a technology called RSDL¹ where the second layer is below the first. When the laser reaches the end of the first layer, it focuses on the inner layer, and scans back towards the centre of the disc.

Since a single DVD can hold up to 17 gigabytes of information, which translates into eight hours of digital video, DVDs have room for:

• Up to eight different audio tracks, for those people who want to work on their French or German while watching their favourite movies.

• Up to nine different camera angles. (Who wants to watch someone talking from the front when you can look at them from overhead or behind?)

• Sub-titles, for those who watch movies with loud kids or friends.

DVD technology has even reached the computer: with DVD-ROM, the replacement for CD-ROM. DVD-ROM is backwards compatible, meaning it can still play CD-ROMs. However, with DVD-ROM you can also watch movies on your computer screen, or cut down on the number of discs it takes to hold a single program or game. Some games that used to take up to five or six CDs will now only need one DVD disc for the game to work.

Regional Locking

Most DVD videos are regionally coded. Each region is assigned a number, which is then encoded into both the DVD players and discs sold in that region. This allows DVD manufacturers to regulate what is seen when a particular movie or software program is released in a given country. In some cases, it also stops viewers in some regions from having all of the extra features that others have access to, such as the film being on only one side of the disc, directors' commentaries and other funky things. The region numbers are:

• 0 - no region lock
• 1 - Canada, USA, USA Territories
• 2 - Japan, Europe, South Africa, Middle East, Egypt
• 3 - Southeast Asia, East Asia, Hong Kong
• 4 - Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, Caribbean
• 5 - former Soviet Union, Indian Subcontinent, Africa, North Korea, Mongolia
• 6 - China
• 7 - reserved²
• 8 - special international venues, such as airplanes and cruise ships

A 'content scrambling system', or CSS, stops people from watching DVDs on unauthorised players. The restriction that CSS imposes is that it prevents you using, say, American DVDs on British players, allowing price fixing³.

Copy Protection

The paranoia of the movie industry doesn't stop with region coding. They insist on multiple levels of copy protection, particularly to stop perfect digital copies being made.

The analogue copy protection system, Macrovision, stops you from making a VHS copy of a DVD. It works by putting colour bursts into the non-picture parts of the TV signal, which confuses the automatic gain controls and synchronization circuits of 95% of video recorders. Unfortunately it can effect some older TVs as well, and in some cases, mess up the picture quality.

Manufacturers of DVD-video machines have learned from past mistakes, and to stop consumers from getting frustrated with attempting to programme the VCR, they didn't include any recording facilities.

Reasons to Get DVD

DVDs are inexpensive and most video stores rent them just like videos. In addition, there is a vast amount of titles and features in DVD video format - and the list is growing.