CD/DVD

It's hard to imagine that in the 1980s the first CD players cost thousands of dollars and were the province of only the wealthy and rabid audiophiles. Today compact discs and compact disc players are found in virtually every environment imaginable-from the home to the workplace to the classroom. They're inexpensive and they are the closest thing we have to a universal format for music media (although the MP3 format is rapidly catching up).

Digital versatile discs (you probably know them better as DVDs) and their players are in much the same situation as CDs and CD players were in the '80s and early '90s. Just as the CD virtually eliminated the demand for vinyl records, so too has the DVD begun to cut deeply into the sale and rental of videocassettes. When recording to the DVD format becomes more affordable, you can be sure that VCRs will disappear entirely.

While CDs and DVDs are best known as entertainment media (for listening to music and watching movies, respectively), you'll see that both media are capable of storing all kinds of information. Click on the questions below to learn more about how CD/DVD technologies work and how they can be used in learning environments.

1. How do CDs and DVDs actually work?
2. What can CDs and DVDs be used for?
3. What are some educational uses for CDs and DVDs?

How do CDs and DVDs actually work?

You've been popping those silver discs into your CD player and listening to music for years, but do you really know how that plastic-encased piece of tinfoil gets turned into audio? We thought not. Read on to learn how CDs and the next generation in optical disc technology, DVDs, actually work.

On the surface, both CDs and DVDs look virtually identical - a laminated disc measuring 120 mm or 5 inches in diameter and 1.2 mm in height that encases a metallic reflective surface - and they do indeed use much the same technology. In both DVDs and CDs, data is stored in microscopic tracks that are made up of pits (indentations) and lands (flats) backed by a reflective material. While one motorized mechanism inside the player spins the disc, another motorized mechanism guides a laser beam that shines on these pits and lands; the reflected light patterns are then read by an optical device that converts these patterns into little bits of data called, appropriately enough, bits. The bits are assembled into the bytes that can in turn represent just about any kind of data imaginable (for example, images or sounds).

One of the great things about both CDs and DVDs is that, unlike vinyl records and magnetic tapes, the playback mechanism never physically touches the storage material, thus eliminating wear and tear. Properly handled CDs and DVDs sound and look as good on the thousandth playback as they did on the first.

DVDs differ from CDs, however, in that they have much, much smaller tracks and have more than one layer of data embedded in the disc. With smaller tracks and additional layers, DVDs are capable of holding quite a bit more data than conventional CDs. Whereas a CD can store up to 700 Megabytes, a single-sided DVD can hold 8 Gigabytes (that's 8,000 Megabytes) and a double-sided one can hold up to 15.9 Gigabytes. Because they can hold such vast quantities of data, DVDs can produce video images and sounds that are superior to CDs, VHS tapes, and laser discs (a short-lived analog video format of the early 1990s). DVDs also often offer multiple soundtracks, subtitles in a variety of languages, and even alternate camera angles.

To learn more about how CDs and DVDs work, follow these links:

DVD Demystified
http://dvddemystified.com/

Howstuffworks.com: CDs
http://www.howstuffworks.com/cd.htm

Howstuffworks.com: DVDs
http://www.howstuffworks.com/dvd.htm

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