It is only eight years since the DVD hit the market, but by the end of this year you may be justified in asking whether it has had its day. By David Hellaby.

If DVD isn?t broken, why fix it?

Later this year we will start to see the emergence of two potential replacements to the humble DVD ? Toshiba?s HD-DVD and Sony?s Blu-ray disc. Just as battles have been fought over VHS and Betamax, there is already a fight raging over which standard will be adopted for the next generation of recording medium.

As the world continues its conversion from analog to digital, there is an insatiable demand for data storage. One of the major drivers in the home entertainment area is the growing area of high-definition (HD) video content, which provides stunningly realistic and detailed images compared to standard definition television.

In order to enjoy HD in your living room, the content has to get to your HD compatible television somehow. One way is to tune it in over the airwaves with a HD digital set-top box. However, future movies will also be available in HD, but the means of transporting it from the video shop to your home is a problem with the current formats available today. Simply put, HD content is massive, and too large for cassettes or even DVD discs. A feature-length HD movie would take about five DVDs to store, and swapping discs throughout a movie just wouldn?t be acceptable.

A single layer HD-DVD disc, on the other hand, can store up to 15GB of data while a dual layer disc will store 30GB. ?Dual layer? essentially means that two ?platters? of information are stored on top of each other on a single-sided disc, and the laser can read the second layer by focusing through the first layer.

This is certainly an improvement over the seemingly tiny 4.7GB of storage of a standard DVD and the 8.5GB of a dual layer disc. By comparison, Blu-ray has a capacity of about 25GB for a single layer disc and 50GB for a dual layer, single sided disc. Sony also recently announced the development of an eight-layer model capable of storing an incredible 200GB. In contrast, HD-DVDs can only support three layers of 15GB, making 64GB is its maximum capacity. Then again, there?s always the question of whether we really need this much storage in the first place. History, however, shows that we as consumers have an insatiable appetite for storage.

Sony has also unveiled the ability to make Blu-ray discs out of paper, which is a technology it developed with the help of Japanese printing specialist Toppan. A 25GB disc, for example, could be made from around 50 percent paper, which reduces the cost of materials to create it, plus it?s more environmentally friendly to dispose of. You can even cut it up with a pair of scissors.

A basic Blu-ray disc can store about two hours 15 minutes of high definition (MPEG 2) video on a single layer and up to four hours 30 minutes on the dual layer variety. Alternatively it can record up to 13 hours of standard definition TV on a single layer disc compared to a maximum of 133 minutes on a DVD.

Despite HD-DVD?s lower data capacity, its supporters initially claimed it can store more actual movie time than Blu-ray because it is capable of utilising advanced MPEG 4 compression techniques. This changed late last year when the Blu-ray Association adopted Microsoft VC-1 codec enabling Blu-ray discs to utilise MPEG 4 compression.