Benjamin Britton, an associate professor and electronic artist at the University of Cincinnati, provides the following explanation:
Image: SONY DISC MANUFACTURING
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. Thus, the DVD makes sense for video and other industries in a way that the CD never could. 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 100 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 3,600 MB. Compare that to the maximum storage space of a CD which is about 640 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. Thus, I need to place it on DVD, and not only on one DVD, but on thousands for distribution.
So I make a single DVD at home and then take my disc to a replication house, such as Panasonic, CinRam, Nimbus or Diner. 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. Let's say I want to make 1,000 DVD versions of my virtual reality artwork or 2 million DVD copies of my latest Hollywood flick. The replication house simply uses the metal stamper to imprint the pattern into the plastic coating of all those DVDs.