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Speaker 1: Marshall Brain with today's question, how do SDR discs work?
Speaker 1: If you've read the how Stuff Works article describing how
Speaker 1: c ds work, then you know that the basic idea
Speaker 1: behind data storage on a normal c D is simple.
Speaker 1: The surface of the CD contains one long spiral track
Speaker 1: of data. Along the track, there are flat, reflective areas
Speaker 1: and non reflective bumps. A flat reflective area represents a
Speaker 1: binary one, and a non reflective bump represents a binary zero.
Speaker 1: The CD drive shines a laser at the surface of
Speaker 1: the c D and can detect the reflective areas and
Speaker 1: the bumps by the amount of laser light they reflect.
Speaker 1: Normal c ds can't be modified. There read only devices.
Speaker 1: A CDR disc needs to allow the drive to write
Speaker 1: data onto the disk. For a CDR disc to work,
Speaker 1: there must be a way for a laser to create
Speaker 1: a non reflective area on the disk. A CDR disc
Speaker 1: therefore has an extra layer that the laser can modify.
Speaker 1: This extra layer contains a greenish dye. In a normal
Speaker 1: c D, you have a plastic substrate covered with a
Speaker 1: reflective aluminum or gold layer. In a CDR, you have
Speaker 1: a plastic substrate, a die layer, and a reflective gold layer.
Speaker 1: When you write data to a CDR, the writing laser,
Speaker 1: which is much more powerful than the reading laser, heats
Speaker 1: up that die layer and changes its transparency. The change
Speaker 1: in the dye creates the equivalent of a non reflective
Speaker 1: bump on the surface of the disk. This is a
Speaker 1: permanent change, and both a CD and a CDR drive
Speaker 1: can read that modified die layer as a bump. Later on,
Speaker 1: it turns out that the dye is fairly sensitive delight.
Speaker 1: It has to be in order for a laser to
Speaker 1: modify it quickly. Therefore, you want to avoid exposing CDR
Speaker 1: discs to sunlight. This podcast is brought to you by
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Speaker 1: more than downloadable titles across all types of literature and
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