CD-ROM

CD-ROMs are a little bit different than floppy and hard disks. Instead of electromagnetism, they use a laser to reflect light off microscopic pits embedded in the disks. When a pit swings by, the light is reflected to an electric eye. Where there is no pit, the light is not reflected. DVD-ROMs store more data. They can do it by having smaller pits, using two levels of pits, one under a translucent surface containing the other layer, and in some cases, by storing data on both sides of the disk.

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