The tools of technology can seem like a confusing alphabet-soup. Terms such as ZIP, CD or DVD are commonly used to describe the means available for storing and sharing information, ranging from text to audio to full-length films. Of them all, DVD, which stands for digital versatile disc, is poised to become the most popular and reliable means for storing data, especially high-quality digital video.
DVDs are now rapidly making their way into American homes as the state-of-the-art entertainment option for watching Hollywood releases. Before going into the mechanics of how a DVD works, it might be best to explain the why. In other words, why is the industry replacing previous storage-unit standards, including the CD short for compact disc?
Quite simply, the DVD's storage capacity is much greater. A high-quality digital video could simply never fit onto a CD. It can't even fit comfortably on a computer hard drive. Indeed, a high-quality digital video requires up to megabytes MB of data space each minute, depending on the amount of compression used. MPEG2, a format commonly used for playing video via computer, compresses one minute of visual data into about 30 MB.
So a two-minute video requires 60 MB, and a two-hour movie requires 3, MB. Compare that to the maximum storage space of a CD which is about MB. The encoding of data onto a DVD may seem like a black art, but it's really not that much different from encoding data onto a videotape.
A videotape stores and plays back information based on the physical placement and arrangement of iron oxide particles on the material of the tape. A DVD similarly stores and plays information based on a particular "dot pattern" on its surface. A very precise laser burns these dots--actually, incredibly small pits--on to the master DVD. It is the smallness of the dots that allows for the roomy storage capacity of the DVD. Practically speaking, let's say I had a virtual reality project of 75 MB on a disc.
If I want to release my project to the public or exhibit it in museums across the country, I'm going to need a reliable means for viewing. Most of the optical industry service providers are, not surprisingly, located on the West Coast.
But there are regional houses as well. They will feed the information from my disc via software algorithms to what is called a burner, which guides the laser that brands a glass-topped DVD with the data pattern of dots that vary in terms of spacing and in terms of brightness and darkness.
The spacing and variation of brightness and darkness of the dots are what makes the data readable to a computer or to a television set DVD player in the same way that the variety of shapes and spacing of these letters and words enables you to read this explanation.
Then, a photograph is taken of this master DVD and an etching is made from that photograph. In turn, the etching is used to create a metal stamper. The replication house simply uses the metal stamper to imprint the pattern into the plastic coating of all those DVDs.
Smaller pits make it possible to store more information on DVDs. What most people find at the local movie rental or video store is called a DVD It's so named because it stores nearly five gigabytes GB of information.
Instead, the machine's motor rotates it, and the player deciphers the data for the entire film by moving in a spiral from the inside to the outside of the disc. The speed at which it moves depends on the disc you're playing. If you're playing a "dual-layer" DVD, once the laser reaches the outside, it reads additional tracks by heading back to the middle of the disc. The DVD player also has a device that controls tracking, moving the laser outward or inward as needed to stay in the correct spot on the disc.
This system makes sure that the laser reads the right data at the right time. It's also the reason you can skip ahead to a new part of a movie just by pressing the "skip track" button on your remote. The device tells the laser where it needs to go. Though a lot of people worry about scratches on the reflective sides of their DVDs, most of the data the DVD player reads is actually deeply embedded and closer to the label side of the disc. The DVD was seen as the next step from the video cassette.
There are many inventions involved to make a DVD possible. First of all, the computer had to be invented. You'll realize this when you try to understand how DVD works. On a DVD disk there is coded in a binary form all the information one needs to record a picture.
From Wikibooks, open books for an open world. Namespaces Wikijunior Discussion. Views Read Edit Edit source View history. Reading room forum Community portal Bulletin Board Help out!
Policies and guidelines Contact us. This Wikijunior article is a stub. You can help Wikijunior by expanding it.
0コメント