In the article How CDs Work, you learn about how patterns of bumps on a mirrored surface can be interpreted as bits. These bits can be assembled into bytes and then played back through an analog-to-digital converter to create music. A CD can hold about 650 megabytes of information or about 75 minutes of music.

A DVD works exactly the same way, but it can hold a lot more information -- about 4.7 gigabytes (about seven times as much as a CD). DVDs can hold more data than CDs because the bumps are smaller and the tracks are closer together, giving DVDs more storage space. Here are the typical contents of a movie stored on a DVD:

  • Up to 133 minutes of high-resolution video in letterbox or pan-and-scan format, at 720 dots of horizontal resolution (The video compression ratio is typically 40:1 under MPEG-2.)
  • Soundtrack presented in up to eight languages using 5.1 channel Dolby digital surround sound
  • Subtitles in up to 32 languages
You can also use DVDs to store music. If you do, you can store almost eight hours of music per side!

MPEG-2 compression is important to the whole scheme, because without a good compression algorithm there's no way a movie could fit on a DVD. See for more information on MPEG.

Here are some interesting links: