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. PhenII 3. That's why they're labeled 4. There is no difference -- none -- between "movie data" and "normal data" on a DVD-R.
Glockjr and Skbenin have it correct -- the discrepancy comes from the way a computer calculates kilo, mega, and gigabytes vs. Computers , on the other hand, calculate in base 2, and the metric definitions of K, M, and G do not fit neatly into powers of 2. Now, for a while, hard drive manufacturers followed the accepted computing definitions, and all was good. Then, somewhere along the line, one of them realized that they could make their products seem to have a higher capacity than the competition simply by reverting to the standard base metric definition and advertising their products' capacity that way.
Since the majority of computer hardware was, by that point, being sold to home and office users who didn't know the difference, instead of to geeks and engineers who wouldn't be fooled, they got away with it, and their competitors quickly followed suit in order to keep up. However, your PC and its operating system still calculate drive capacity based on the base-2 definitions.
Therefore, what the manufacturers call a 4. If in doubt, Google it. In a related question, why is it when you use UDF packet writing i. Not complaining, just wondering why. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Sal Prince. Sal Prince is a former Lifewire writer and a video production professional and tech enthusiast who has written extensively about electronics and DVRs.
Updated on May 01, Tweet Share Email. Was this page helpful? Thanks for letting us know! Email Address Sign up There was an error. In our study, we showed how to break this fundamental limit by using a two-light-beam method, with different colours, for recording onto discs instead of the conventional single-light-beam method.
But we gave the two beams different functions:. The two beams were then overlapped. As the second beam cancelled out the first in its donut ring, the recording process was tightly confined to the centre of the writing beam. This new technique produces an effective focal spot of nine nanometres - or one ten thousandth the diameter of a human hair. Our work will greatly impact the development of super-compact devices as well as nanoscience and nanotechnology research.
The exceptional penetration feature of light beams allow for 3D recording or fabrication, which can dramatically increase the data storage - the number of dots - on a single optical device.
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