Optical disc

In computing and optical disc recording technologies,[1] an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum,[2] on one of its flat surfaces. Its main uses are physical offline data distribution and long-term archival. Changes from pit to land or from land to pit correspond to a binary value of 1; while no change, regardless of whether in a land or a pit area, corresponds to a binary value of 0.

The optical lens of a compact disc drive.
The bottom surface of a 12 cm compact disc (CD-R), showing characteristic iridescence.
LaserCard made by Drexler Technology Corporation.

Non-circular optical discs exist for fashion purposes; see shaped compact disc.

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