💯 The Difference of CD, DVD and Blu-Ray Technologies Explained. Watch this Video to Find out! #1

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Structure of a Digital Disc
CDs, DVDs, and Blu-ray discs are three media that can store digital data. They each consist of a metal layer sandwiched between two plastic layers. Data is stored in a spiral-shaped groove that starts near the centre of the disc.

Encoding Data
To store sound information on a disc, it must first be broken into samples and encoded in binary digits. To write information onto a disc, a laser is used to burn little pits into the metal layer. Pits represent a 1, and a flat surface represents a 0.

The capacity of a Disc
The amount of information that can fit on the disc depends on the size of the pits burned into it. CDs, DVDs, and Blu-ray discs each use different lasers, which make different pits. This is why they store different amounts of data.

Compact Discs
A CD uses an infrared laser with a wavelength of 780 nm to read and write data. Music burned to a CD is sampled at 44.1 kHz. This equates to about 75 minutes of uncompressed music or 650 MB of data.

Digital Versatile Discs
A DVD uses a red laser with a wavelength of 656 nm to read and write data. This lets them store 4.7 GB of data; that is, about 4 hours' worth of high-quality video. Sound in a movie stored on a DVD is sampled at 192 kHz.

Blu-ray Discs
Blu-ray discs use a blue laser with a wavelength of 405 nm to read and write data. They can store 25 GB of data – more than 5 times as much as a DVD! This allows them to store movies with higher definition than DVDs.

Reading from a CD
When a CD is played, a laser shines onto its surface to determine its contents. When the laser strikes a flat part of the disc, representing a 0, it reflects normally. When it strikes one of the tiny pits, representing a 1, it scatters.

Decoding the Data
The 1s and 0s of the disc are fed to a digital-to-analog (D/A) converter. This device reconstructs the original sound wave as a voltage that varies with time. The voltage can then be applied to a speaker to reproduce the sound.

Other Types of Disc
DVDs and Blu-ray discs are read by lasers of other wavelengths. The data they contained is more densely-packed and more complicated than simple sound data. This data must be interpreted by a computer.