095 - What is Media Disc

A Disc or optical disc is an electronic data storage medium that can be write and read using a low-powered laser beam. Disc is a flat, glossy and round plate on which data can be encoded. Disc is the main material for copying or burning data. Types of Disc: Compact Disc (CD), Digital Versatile Disc (DVD), Blu-ray Disc (BR).

An optical disc is a flat disc that stores data in the form of pits along a spiral groove within its surface. The disc, usually made of polycarbonate, has a reflective coating often consisting of aluminum. The data are generally accessed when the reflective surface is illuminated with intense light, usually in the form of red or blue laser light-hence the name optical disc.

A computer's peripheral device used to read or write an optical disc is called an optical disc drive (ODD). The disc is rotated rapidly, and a laser is reflected off the disc to an optical sensor, which is sampled periodically. If the laser strikes the flat area between pits, the sensor picks up the reflection and registers the digital value 1. If the laser strikes one of the pits, it is deflected from the sensor, and the sample value is a digital 0. The computer convert the digital value into a data such as text, image, audio or video.

Following are the major types:

Compact disc (CD) • Capacity: Typically up to 700 MB
Digital Versatile Disc (DVD) • Capacity: DVD 4.7 GB, DVD DL 8.5GB, HD DVD 15GB and HD DVD DL 30GB.
Blu-ray Disc (BD) • Capacity: BD 25GB, BD DL 50GB, BD XL 100GB and 128GB.

Read-Only (ROM) • Read-only discs are pressed from a master at the time of manufacture and cannot be erased. They include the CD-music, CD-ROM, DVD-Video, DVD-ROM, BD-games and BD-ROM.
Write-Once or Recordable (R) • R discs are burnable that can be recorded in the user's environment but cannot be erased. They include the CD-R, DVD-R, DVD+R, BD-R, WORM discs, as well as magneto-optic (MO) discs in WORM mode.
Rewritable (RW) Recordable Erasable (RE) • RW RE discs are burnable that can be written and re-written numerous times. Employing phase change technology, consumer-oriented products include CD-RW, DVD-RAM, DVD-RW, DVD+RW and BD-RE.
Dual Layer (DL) • Dual Layer disc is double layer format that can double the total disc capacity. They include the DVD+R DL, DVD-R DL, BD+R DL, BD-R DL.

A plus (+) format has some advantages over minus (-) format in terms of error checking, better tracking and speed control resulting in more reliable media, additional session linking methods which results in fewer damaged discs. Most of the differences are very technical in nature, but allow for faster writing speeds and more rewrites without errors. A plus format is more reliable because it was released later, but more drives are compatible with the minus format.

Disc is also known as: optical disc, optical media or optical storage.

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