WEBVTT - How do CD-R discs work?

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<v Speaker 1>That's Audible podcast dot com slash brain Stuff. Hi Im

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<v Speaker 1>Marshall Brain with today's question, how do SDR discs work?

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<v Speaker 1>If you've read the how Stuff Works article describing how

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<v Speaker 1>c ds work, then you know that the basic idea

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<v Speaker 1>behind data storage on a normal c D is simple.

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<v Speaker 1>The surface of the CD contains one long spiral track

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<v Speaker 1>of data. Along the track, there are flat, reflective areas

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<v Speaker 1>and non reflective bumps. A flat reflective area represents a

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<v Speaker 1>binary one, and a non reflective bump represents a binary zero.

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<v Speaker 1>The CD drive shines a laser at the surface of

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<v Speaker 1>the c D and can detect the reflective areas and

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<v Speaker 1>the bumps by the amount of laser light they reflect.

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<v Speaker 1>Normal c ds can't be modified. There read only devices.

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<v Speaker 1>A CDR disc needs to allow the drive to write

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<v Speaker 1>data onto the disk. For a CDR disc to work,

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<v Speaker 1>there must be a way for a laser to create

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<v Speaker 1>a non reflective area on the disk. A CDR disc

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<v Speaker 1>therefore has an extra layer that the laser can modify.

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<v Speaker 1>This extra layer contains a greenish dye. In a normal

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<v Speaker 1>c D, you have a plastic substrate covered with a

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<v Speaker 1>reflective aluminum or gold layer. In a CDR, you have

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<v Speaker 1>a plastic substrate, a die layer, and a reflective gold layer.

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<v Speaker 1>When you write data to a CDR, the writing laser,

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<v Speaker 1>which is much more powerful than the reading laser, heats

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<v Speaker 1>up that die layer and changes its transparency. The change

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<v Speaker 1>in the dye creates the equivalent of a non reflective

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<v Speaker 1>bump on the surface of the disk. This is a

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<v Speaker 1>permanent change, and both a CD and a CDR drive

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<v Speaker 1>can read that modified die layer as a bump. Later on,

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<v Speaker 1>it turns out that the dye is fairly sensitive delight.

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<v Speaker 1>It has to be in order for a laser to

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<v Speaker 1>modify it quickly. Therefore, you want to avoid exposing CDR

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<v Speaker 1>discs to sunlight. This podcast is brought to you by

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