How optical discs are similar

Storage: Optical Discs

An entirely different method of recording data is used for optical discs. These include the various kinds of CD and DVD discs.

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You may guess from the word "optical" that it has to do with light. You'd be exactly right! Laser light, in fact. Optical discs come in several varieties which are made in somewhat different ways for different purposes.

• Formed of layers
• Data in a spiral groove on starting from the center of the disc
• Digital data (1's and 0's)
• 1's and 0's are formed by how the disc absorbs or reflects light from a tiny laser.

The different types of optical discs use different materials and methods to absorb and reflect the light.

How It Works (a simple version)

An optical disc is made mainly of polycarbonate (a plastic). The data is stored on a layer inside the polycarbonate. A metal layer reflects the laser light back to a sensor. To read the data on a disc, laser light shines through the polycarbonate and hits the data layer. How the laser light is reflected or absorbed is read as a 1 or a 0 by the computer.

In a CD the data layer is near the top of the disc, the label side.

In a DVD the data layer is in the middle of the disc. A DVD can actually have data in two layers. It can access the data from one side or from both sides. This is how a double-sided, double-layered DVD can hold 4 times the data that a single-sided, single-layered DVD can.

Дата добавления: 2014-12-23