Blu-ray and HD-DVD (High-Density Digital Versatile Disc) are the two next-generation optical disc format designs to be the successors to the standard DVD format. Both are the same size as conventional CDs and DVDs, however the primary difference is the amount of data that can be stored on a single disc. Using 405nm wavelength blue lasers, Blu-ray can store 25GB per layer and HD-DVD can store 15GB per layer.

History

Philips's started the development of the Laserdisc in 1969 and many of the technologies Sony carried over and adopted when they partnered with Philips to create the CD back in 1979. In the early 1990s both companies joined forces once again to work on a new high-density disc called the MultiMedia Compact Disc (MMCD), but their format was eventually abandoned in favour of Toshiba's competing Super Density Disc (SD). SD had the vast majority of supporters at the time, such as Panasonic, Mitsubishi, Pioneer, Hitachi, and Time Warner.

These two factions eventually cut a deal, brokered by IBM president Lou Gerstner, on a new format: DVD. Toshiba came out on top in the end, and Sony and Philips were largely left out of the royalties.

Immediately there after Sony and Philips started work on a next-generation system, the Professional Disc for DATA (PDD or ProDATA). This was based on an optical disc system Sony had already been developing on the side, and would eventually become Blu-ray. Toshiba also started work on a next-generation system, the Advanced Optical Disc, which eventually evolved into the HD-DVD.

Technical differences

Both systems use the same kind of 405nm wavelength blue-violet laser, were as standard DVD format uses a red 650nm laser. Due to its shorter wavelength (405nm), substantially more data can be stored on a HD-DVD and Blu-ray disc. However, the two disc formats are very different in two distinct ways. The numerical aperture of the optical pick-up head is 0.65 for HD-DVD and 0.85 for Blu-ray, making them incompatible with each other despite using the same type of lasers. Since the Blu-ray disc has a tighter track pitch, it can hold more pits on the same size disc compared to HD-DVD. Hence a HD-DVD can store up to 15GB on a single layer disc and 30GB on a dual layer disc and Blu-ray can store 25GB on a single layered disc and 50GB on a dual layer disc.

The second biggest difference between the two disc formats are the different surface layers (the clear plastic layer on the surface of the data). HD-DVD uses a 0.6mm thick surface layer, the same as a DVD. Blu-ray has a much smaller layer, 0.1mm, to help enable the laser to focus with that 0.85 aperture.

Cost

Because HD-DVD uses the same plastic layer that DVDs use, the cost of manufacturing the discs are greatly reduced compared to Blu-ray discs. In order to produce Blu-ray discs costly production facilities need to be modified or replaced in order to produce the discs. A special hard coating is also applied to Blu-ray discs to protect the data on the disc. This coating is not needed with HD-DVD discs. In short, Blu-ray discs are more expensive, but are able to hold more data.

Compatibility

While there is no direct compatibility between HD-DVD and Blu-ray there are many compatibility options available. Many new Blu-ray and HD-DVD players support both DVD and CD playback. LG has also produced a player that is capable of playing both Blu-ray and HD-DVD formats and consumers can expect other hardware manufacturers to follow. A popular option for movie studios is double-sided discs were you can use your standard DVD player to play one side of the disc and HD-DVD or Blu-ray players to play the other side. This allows consumers to use there current hardware without incurring the expense of costly upgrades.

All these compatibility options are not guaranteed and it is up to consumers to ensure what they are buying before taking it home. It is also advisable to know what you want to purchase before you go shopping. If you have a large CD and DVD collection and are interested in buying a Blu-ray or HD-DVD player, then it is a good idea to ensure it will play your existing collection and not just assume that it will play everything.