The CCD (Charge-Coupled Device) is a type of semiconductor that can store packets of electrical charge in tiny surface regions called potential wells. Because of the way the device is constructed, the packets of charge can be moved from place to place within the semiconductor without rearranging their order; thus, the electronic "information" is stored until it is needed.

There are three basic ways in which information can be stored in a CCD. First, since the amount of charge in an individual well can be anywhere from zero to maximum, the CCD can be used as an analog storage device. The potential wells can also be thought of as being either empty or full (off or on); in this way the CCD can be thought of as a digital device. Finally, if a light source is focused upon the CCD's surface, the wells will fill according to the...