The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc storage format. It is designed to supersede the DVD format and is capable of storing several hours of high-definition video (HDTV 720p and 1080p). The main application of Blu-ray is as a medium for video material such as feature films and the physical distribution of video games for the PlayStation 3, PlayStation 4, PlayStation 5, Xbox One, and Xbox Series X. The name "Blu-ray" refers to the blue laser (which is a violet laser) used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.
Building a Blu-ray Disc:
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:
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 a space on the disc to avoid recording over a program
access the Web to download subtitles and other extra features
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 (which is where the format gets its name). A blue laser has a shorter wavelength (405 nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are only 0.15 microns (µm) (1 micron = 10-6 meters) long -- this is more than twice as small as the pits on a DVD. Plus, Blu-ray has reduced the track pitch from 0.74 microns to 0.32 microns. The smaller pits, smaller beam and shorter track pitch together enable a single-layer Blu-ray disc to hold more than 25 GB of information -- about five times the amount of information that can be stored on a DVD.
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.
How Does a Blu-Ray Disc Work?
Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a blue laser. A blue laser has shorter wavelengths (405 nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are only 0.15 microns long. This is more than twice as small as the pits on a DVD.
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 0.6mm polycarbonate layers. 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 not perpendicular to the beam, it can lead to a problem known as disc tilt where the laser beam is distorted.
The Blu-ray disc overcomes DVD-reading issues by placing the data on top of a 1.1 mm thick polycarbonate layer. Having the data on top prevents birefringence and therefore prevents readability problems. And, with the recording layer sitting closer to the objective lens of the reading mechanism, the problem of disc tilt is virtually eliminated. Because the data is closer to the surface, there is a hard coating on the outside of the disc to protect it from scratches and fingerprints.
What Type of File System Is Used by Blu-ray Discs?
The name of the file system that is used by Blu-ray discs is called UDF, which is short for Universal Disk Format. While usage of UDF is most prevalent when it comes to DVDs, it is also used for newer optical disc formats.
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