Around the late 1990s, a new Disc technology emerged that revolutionalised digital sound and video to greater highs. It was called DVD, and it greatly impacted itself on the film industry. The industry is set for yet another revolution with the introduction of Blu-ray Discs (BD) in 2006. With their high storage capacity, Blu-ray discs can hold and play back large quantities of high-definition video and audio, as well as photos, data and other digital content. When compared, a single-sided, standard DVD can hold around 4.7 GB (gigabytes) of information. An average two-hour, standard-definition movie with a few extra features. But a high-definition movie, which has a much clearer image, requires up to five times more bandwidth and therefore requires a disc with about five times more storage. As TV sets and movie studios made their move to high definition, consumers were also obliged to do likewise, this was because of the need for playback systems with a lot more storage capacity. Blu-ray is regarded as the next-generation digital video disc. It can record, store and play back high-definition video and digital audio, as well as computer data. The advantage to Blu-ray is the absolute amount of information it can hold. This technology is quite amazing. A single-layer Blu-ray disc, which is roughly the same size as a DVD, can hold up to 27 GB of data, that’s more than two hours of high-definition video or about 13 hours of standard video. A double-layer Blu-ray disc can store up to 50 GB, enough to hold about 4.5 hours of high-definition video or more than 20 hours of standard video. And there are even plans in the works to develop a disc with twice that amount of storage (100GB). Blu-ray discs not only have more storage capacity than traditional DVDs, but they also offer a new level of interactivity. Users will be able to connect to the Internet and instantly download subtitles and other interactive movie features. With Blu-ray, you can do any of the following; record high-definition television (HDTV) without any quality loss instantly skip to any spot on the disc, record one program while watching another on the disc, create playlists, edit or reorder programs recorded on the disc, automatically search for an empty space on the disc to avoid recording over a program, access the Web to download subtitles and other extra features, etc. Discs store digitally encoded video and audio information in pits spiral grooves that run from the centre of the disc to its edges. A laser reads the other side of these pits , the bumps to play the movie or program that is stored on the DVD. The more data that is contained on a disc, the smaller and more closely packed the pits must be. The smaller the pits (and therefore the bumps), the more precise the reading laser must be. Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a blue laser (maybe that why they are called Blu-ray for blue ray). A blue laser has a shorter wavelength (405 nanometres) than a red laser (650 nanometres). Each Blu-ray disc is about the same thickness (1.2 millimetres) as a DVD. But the two types of discs store data differently. In a DVD, the data is sandwiched between two polycarbonate layers, each 0.6-mm thick. Having a polycarbonate layer on top of the data can cause a problem called birefringence, in which the substrate layer refracts the laser light into two separate beams. If the beam is split too widely, the disc cannot be read. Also, if the DVD surface is not exactly flat, and is therefore not exactly perpendicular to the beam, it can lead to a problem known as disc tilt, in which the laser beam is distorted. All of these issues lead to a very involved manufacturing process. eddie@afrowebs.com
