Blu-ray is a cutting-edge, high-definition optical disc that can store significantly more data than a standard DVD. A single-layer Blu-ray disc can store approximately 25 gigabytes of data: five times the amount of a standard single-layer DVD. Dual-layer Blu-ray discs can store twice the amount as single-layer discs, and about eight times the amount of a standard dual-layer DVD.
A standard DVD contains enough space for a two-hour, non-high-definition movie, plus a few extra features. A Blu-ray disc allows enough space for 13 hours of standard footage or two hours of high-definition video. In addition, Blu-ray discs allow you to skip instantly anywhere on the disc; record one show while watching another; edit and reorder the footage on the disc; and access the web to download subtitles and other extras.
All DVD’s and CD’s store information as a series of grooves on the recording surface of the disc. The grooves are written in a spiral that winds from the center of the disc to the outside edge. On one side, the grooves appear as pits; on the other, they stand out as bumps. To read the disc, a player shines a laser over the bumpy side of the disc. The bumps cause the laser to bounce back and register on a sensor.
Standard CD and DVD players use a red laser to read the information on a disc. Blu-ray compatible players use a blue laser. Blue light has a shorter wavelength than red light. This makes the laser itself more sensitive and capable of detecting much smaller grooves than a red laser can.
Because the blue laser can detect smaller grooves, the information on a Blu-ray disc can be written much smaller than on a standard disc. This is why a Blu-ray disc can contain so much more information than a standard CD or DVD, even though the discs are the same size.
Blu-ray discs are constructed differently than standard discs. These differences in construction eliminate some of the design flaws in standard DVD’s. One of these flaws is birefringence. In a standard DVD, the recorded data is set between two polycarbonate layers. The laser must shine through a layer of polycarbonate in order to reach the data.
Occasionally, the polycarbonate can split the laser into two beams instead of allowing it to penetrate, making the player unable to read the disc. The process of lining up the polycarbonate layers must be done with great precision to prevent birefringence. In addition, the laser beam can become distorted if the disc is not perfectly level inside the player, a problem called “disc tilt.”
On a Blu-ray disc, the data is printed on top of the polycarbonate layer. With the data on top, the laser does not have to shine through polycarbonate in order to read it—and the problem of birefringence is eliminated. This simplifies the manufacturing process, and keeps the cost of Blu-ray discs down. In addition, the data’s location brings it closer to the lens that reads the laser. This makes disc tilt much less of an issue.
Blu-ray stores more data, reads more clearly, and provides interactive features you can’t get on a standard DVD. There aren’t many drawbacks to Blu-ray, but there are a few.
Blu-ray discs require different equipment to manufacture. Despite the ease of making these discs in comparison with standard DVD’s, manufacturers still have to invest in new machinery to make them. This may give a slight edge to Blu-ray’s major competitor: HD-DVD. HD-DVD is another type of high-definition DVD that can be manufactured using the same equipment used for standard DVD’s. It stores less information, but it’s also less expensive.
Blu-ray discs aren’t more expensive than standard discs, but Blu-ray players tend to be significantly more expensive than HD-DVD players. You can buy players that will play standard formats along with either HD-DVD or Blu-ray, but no player can read both HD-DVD and Blu-ray.
Both HD-DVD and Blu-ray have strong support in the market, but neither one has yet gained an edge over the other. Like format wars of past eras, many consumers are reluctant to invest in an expensive new player when they don’t know if the format they choose will survive. However, Blu-ray is a strong contender, and it just might emerge victorious.
