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The popular DVD technology now uses a red laser with a wavelength of 65nm and a focusing lens with a digital aperture of .6, and the disc thickness is .6 mm.. Its capacity is only 4.7GB, even the best double-sided double-layer is only 17GB.
Blu-ray Disc (BD-ROM) technology uses a blue-violet laser with a wavelength of 45nm. Through a digital aperture with a ratio of .85 on a wide-angle lens, it successfully reduces the focused spot size. Moreover, the disc of Blu-ray disc adopts a new optical transparent protective layer with a thickness of .1mm, so as to reduce the chance of abnormal reading or writing or errors caused by tilting during the rotation of the disc, which makes it easier to read the disc data and provides the possibility for greatly improving the storage density.
The track pitch of Blu-ray disc is reduced to .32mm, which is only half of the current DVD (using red light); The minimum diameter of its recording unit-groove (or chemical phase change unit) is .14mm, which is much smaller than the .4mm groove of the current DVD disc. The storage capacity of a single-sided single-layer Blu-ray disc is defined as 23.3GB, 25GB and 27GB, of which the highest capacity (27GB) is more than 2 GB higher than that of the single-sided single-layer disc of the popular red DVD, which is enough to store HDTV content of high-definition TV with a playing time of more than 2 hours or standard TV programs with a playing time of more than 13 hours (VHS image quality, 3.8MB/s). This is only a single-sided and single-layered capacity, and Blu-ray discs are also single-sided and double-layered, which makes the capacity more impressive. Now, double-layer Blu-ray discs with a capacity of about 5GB, such as Matsushita, Hitachi and SONY, have also appeared. The new technology of Blu-ray Disc has a data transmission rate of 36MB/s, and MPEG-2 is adopted as the compression method of streaming media, so as to be compatible with global digital broadcasting standards.
technically speaking, the next generation storage technology of Blu-ray disc is quite advanced. However, because the Blu-ray disc format itself is not compatible with the existing red DVD format, manufacturers who adopt the Blu-ray disc format must make great efforts to replace the whole production line, which greatly increases the production cost of manufacturers and makes its price generally high, which greatly hinders the popularization of Blu-ray disc format. So although Blu-ray technology has been supported by many big manufacturers, the price is the achilles heel of Blu-ray technology.
At present, Mitsubishi of Japan has started to sell the Blu-ray Disc product with model BR23V1. The single-sided storage of this product has reached 23GB, which can provide 2-12 hours of high-definition movies according to the different storage quality, and the highest data transfer rate reaches 36Mbps. In addition, Mitsubishi also cooperated with Sony to launch a Blu-ray disc with a diameter of 8 cm, which is slightly smaller than the conventional Blu-ray disc with a diameter of 12 cm, and the amount of data stored is also smaller, about 15G.
The HD-DVD camp is opposite to Blu-ray. Toshiba originally joined the Blu-ray camp, but the distribution of benefits and related technical characteristics induced Toshiba to quit the organization. In August 22, two companies, Toshiba and NEC, jointly published the AOD(Advanced Optical Disc) technology, which was renamed HD DVD with the full support of DVD-Forum.
HD-DVD is also based on 45nm blue-violet laser storage technology. It adopts the same spiral recording mode as existing DVD and Blu-ray disc, but the track pitch of DVD is reduced from .74μm to .34μm or .4μm, further shortening the length of pit. Physically, the recording density can be improved by reducing the track gauge and the length of pit and shortening the laser wavelength. HD-DVD discs are initially classified as read-only and rewritable. The read-only type has a single layer of 15GB and a double layer of 3GB；. Single-sided double-layer replicable 2GB, single-sided double-layer 4GB. Compared with DVD, it is greatly improved, but compared with Blu-ray disc, the technical gap is still not small. However, the image compression technology used in HD-DVD is not MPEG-2 or MPEG-4, but WMV-HD and H.264 format. Compared with it, the biggest advantages are high compression ratio and low patent fee. If MPEG-4 decoding program is used, each driver needs to pay a high patent fee of two dollars, while if H.264 is used, it only needs to pay .4 dollars, which can reduce the cost for manufacturers. HD-DVD maintains good compatibility, and manufacturers don't have to change the whole production line, just adjust the laser head and control chip to meet the requirements of HD-DVD. In this way, HD-DVD combines the advantages of high storage density of Blu-ray disc, and manufacturers have strong competitiveness without paying high patent fees.