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Both CDs (compact discs) and DVDs (digital versatile discs or digital video discs) are specialized media that store digital information. The most common and inexpensive forms of CDs and DVDs available are read-only in that once data is written onto them, it can only be read back and can not be modified. However, one can easily find write-once discs as well as discs that allow for writing and erasing multiple times. The physical storage principle is to create patterns in the disc material with different reflectivity — this then modifies the reflection of a laser beam that scans across the surface. |
View of a CD or Compact Disc |
| A DVD is similar to the a CD but with a much higher storage density. A DVD holds a minimum of 4.7GB of data and a maximum of 17.1GB of data, which is enough to store a full-length movie and other multimedia presentations that combine sound with graphics. One of the best features of DVD drives is that they are backward-compatible with CD-ROMs, meaning they can play old CD-ROMs, CD-I disks, and video CDs, as well as new DVD-ROMs. Newer DVD players can also read CD-R disks. |  Partial View of a DVD or Digital Versatile Disc
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