1. The Disc Structure:
* Substrate: A thin, rigid disc of polycarbonate plastic forms the base.
* Reflective Layer: A thin layer of aluminum or gold is deposited on the substrate. This layer acts as a mirror, reflecting the laser beam.
* Protective Layer: A clear, protective layer of lacquer is applied over the reflective layer to protect the disc from scratches and dust.
2. Data Encoding:
* Pits and Lands: The data is encoded by creating tiny depressions (pits) and flat areas (lands) on the reflective layer. The arrangement of these pits and lands represents the binary code (0s and 1s) that constitutes the digital data.
* Spiral Track: These pits and lands are arranged in a continuous spiral track that winds across the entire disc. The laser beam follows this spiral track to read the data.
3. Data Reading:
* Laser Beam: A laser beam is focused on the reflective layer of the disc.
* Reflection: When the laser beam hits a land, the light is reflected directly back to the sensor. When the laser beam encounters a pit, the light is scattered and less is reflected back.
* Binary Interpretation: The sensor interprets the varying intensity of reflected light as 0s (pits) and 1s (lands), reconstructing the digital data.
4. Different Optical Disc Types:
* CD (Compact Disc): Uses a red laser with a wavelength of 780 nm. The pits and lands are larger and spaced farther apart compared to DVD and Blu-ray.
* DVD (Digital Versatile Disc): Uses a red laser with a wavelength of 650 nm. The pits and lands are smaller and closer together than on CDs, allowing for higher data density.
* Blu-ray Disc: Uses a blue-violet laser with a wavelength of 405 nm. The pits and lands are even smaller and closer together, enabling the highest data density among the three types.
Key Points:
* Data is encoded by varying the distance between the pits and lands.
* The laser beam reads the data by detecting variations in light reflection.
* Different types of lasers are used for different types of optical discs, allowing for different data storage capacities.
In summary, optical discs store data by creating tiny indentations (pits) and flat areas (lands) on a reflective layer. These pits and lands are arranged in a spiral track and are read by a laser beam, which interprets the variations in light reflection as binary data.
