快猫短视频

THE VHS-versus-Betamax videotape wars of the late 1970s will seem like a schoolyard squabble compared to the three-way battle that is about to be fought over the next generation of high-capacity recordable DVDs.

Unlike recordable CDs, which can hold as much data as a pressed disc from a factory, today鈥檚 recordable DVDs cannot match the data capacity of their factory-made counterparts. Crucially, their maximum capacity of 4.7 gigabytes is not enough for a feature-length movie at full DVD quality.

Initially, the fight to expand this capacity looked like a straight showdown between consumer electronics companies on one side and the major computer makers on the other. The electronics firms are developing a system called Blu-Ray, while the computer makers are backing High Definition DVD (HD-DVD), which is cheaper to make. While both systems use blue laser light to record DVDs and play them back, discs recorded on one system won鈥檛 play on the other.

Then, two weeks ago, at the CeBIT technology fair in Hannover, Germany, a surprise third contender joined the fray. Called 鈥渄ual layer/double time鈥� it uses a red laser, and unlike its rivals will reach the shops within weeks. Better still, discs recorded on the new system can be played back on the millions of DVD players already in use.

All standard DVD players have a feature called dual-layer playback. This allows the data on pre-recorded discs to be split into two separate sections which are stamped into the recording material at slightly different depths. This gives pre-recorded DVDs a total capacity of 8.5 gigabytes. When the data on one layer has been played, the laser in the player shifts focus to the second layer and carries on playing. To most viewers the shift is almost imperceptible.

Dual-layer technology has so far only been used for pre-recorded movie discs pressed in factories. But Philips has found a way to use a red laser to burn dual-layer DVD recordings in a home recorder or PC burner. The first PC burner is expected to go on sale in a few weeks for 鈧�169. Stand-alone decks will be on sale before 2005.

Dual-layer blank discs for the system will eventually cost around 1.5 times as much as today鈥檚 single-layer blanks, according to Philips. Single-layer blanks only cost $1 now and the price is falling. So recording to DVD will soon be cheaper than recording on VHS tape, with longer running times, better pictures and a lot less hassle.

The systems that use blue lasers have different advantages. By exploiting the tight focusing made possible by the short wavelength of blue light, they can read and write data bits far closer together on the recording surface, and so can store far more data on a disc. This will allow discs to hold a full-length movie at far higher quality than is possible even with today鈥檚 pre-recorded discs.

All the leading consumer electronics companies, led by Philips, Sony, Panasonic and Sharp, have been developing Blu-Ray. In this system, the clear plastic layer that protects the recording surface is just 0.1 millimetres thick. This minimises optical distortion if the disc becomes slightly warped during manufacture or use 鈥� which is very common. Blu-Ray stores 25 gigabytes. But because the discs are constructed in a completely different way from today鈥檚 DVDs, new manufacturing equipment will be needed to produce them, making a switch to Blu-Ray very costly.

To cut the cost, computer makers Toshiba and NEC came up with HD-DVD, which has the big advantage that discs can be manufactured using modified versions of the equipment used to make standard DVDs. But the trade-off is that, like today鈥檚 DVDs, the discs must have 0.6 millimetres of clear plastic above the recording layer. Because the laser has to see through this thickness of plastic, any warping creates much more of a problem. To allow for this, the data bits cannot be packed so closely together, reducing HD-DVD鈥檚 storage capacity to about 20 gigabytes per side.

After a year of debate, and growing support from Microsoft, IBM and Intel, HD-DVD recently won the blessing of the DVD Forum, which sets standards for all DVD formats, as the official follow-up to DVD. The Blu-Ray group is pressing ahead with its launch anyway, in the hope that its higher capacity will win the day.

This confusing standards battle will dismay people waiting for an affordable, high-capacity replacement for their VHS recorders. But as discs from the blue laser systems will not play on today鈥檚 DVD players, industry observers say the new red-laser format could well have the edge.

Let the battle commence.