Both Blu-ray and HD-DVD use the same kind of 405 nanometer wavelength blue-violet laser. That means both can focus more sharply than the 650 nanometer red lasers used in current DVD players, and so both can store much more information on the same surface area of a disc.

But there are important differences between them.

Blu-ray packs data into a tighter single spiral on the surface of a disc than HD-DVD. That means a single disk can carry more digital “pits” – the tiny zeroes and ones that are translated into audio and digital content when a disc is played.

That means that a Blu-ray discs can carry more information "per layer" (or, if you like, "spiral"). But it also makes the two formats incompatible.

A standard double-layer DVD has 9 gigabytes (GB) capacity. HD-DVD is capable of holding 30GB of data – or a full-length high-definition movie, plus extras – on a double-layer disc, but Blu-ray launched with 50GB capacity.

It means that the two competing systems must use a different coating on their discs – HD-DVD uses a surface layer that is 0.6mm thick. Blu-ray’s is much thinner at 0.1mm.

This is the root of what makes Blu-ray more expensive to produce – the thinner surface means standard DVD plants need to be re-tooled. A special hard coating must also be added to protect the information stored on a disc’s surface.

Blu-ray is the more sophisticated format – and is being hailed as a “leapfrog” technology. That advance comes at a price, however.

The theory is borne out by a (very) quick search on the internet to compare prices of HD DVD players and their Blu-ray peers.

The cheapest Blu-ray player weighs in at about £450 (£399 if you count Sony’s PlayStation 3 console, which comes with Blu-ray on board). The cheapest HD-DVD player costs about £220 (or £110, if you count the add-on HD-DVD player for Microsoft’s Xbox 360 games console - though to use it, you must already have bought an Xbox 360, which now retails from about £180).

If you are willing to take the plunge and invest in a Blu-ray or HD-DVD player despite the current uncertainty over which will last the course, remember that though both will work with most new TVs, you will need a high definition TV with 1080 screen resolution to get the most from your player.

Most HD-DVD and Blu-ray players will play standard DVDs.

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