Optical storage device

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Key points

  • Optical storage stores data on a reflective disc. Data is read from the disc by bouncing a laser light off the disc surface and measuring the strength of the response. A reflected signal will either give a strong reading or a weaker reading, allowing the disc to represent bits of data.
  • In ROM forms of optical storage, the disc is stamped in a factory. The "pits" in the surface cause a less intense reflection, which is detected as a bit.
  • In recordable forms of optical storage, the disc is written by a strong laser, which changes the colour of the dye on the reflective surface. The difference in the colour changes the intensity of the reflection, acting in the same way as pits on a optical ROM disc do.
  • In rewritable disc, a metal alloy is melted, which changes its reflectivity. A stronger laser can be used to reset the metal back into a its original form. This allows the disc to be changed more than once.
  • Optical storage uses disc-based medium. The disc is spun in the drive and data is read in a groove pattern from the outside of the disc inwards. The laser is on a movable head, which can move in and out across the length of the disc. This makes it easy for any part of the disc to be reached very quickly.

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