Optical Disk

An optical disk is a compact disk or CD. The formatting of the optical disk will dictate whether it is a DVD, CD, read-only or rewritable. Optical disks have replaced vinyl records, cassette tapes, videotapes and floppy disks.

The optical disk became the preferred medium for music, movies and software programs because of its many advantages. Compact, lightweight, durable and digital, the optical disk also provides a minimum of 650 megabytes (MB) of data storage. A double-layered and double-sided DVD optical disk holds up to 15.9 gigabytes (GB) of data.

The optical disk is so named because its technology is based on light. As the disk spins, a laser beam follows a spiraling trail of pits and lands in the plastic material of the disk. The pits reflect light differently than the lands, while a device translates the reflective difference to bits of "on/off" or 1 and 0. The bits form bytes that carry the digital code of the data stored on the optical disk.

A standard optical disk measures 4.724 inches (120 mm) in diameter and .0472 inches (1.2 mm) in thickness. It is made from polycarbonate with a reflective layer of aluminum, coated in lacquer. The master optical disk is made from glass. Nickel stampers are produced from the glass master and used in an injection-molding machine to "press" or produce multiple copies of the optical disk for distribution. If the disk is double-layered, there will be stampers for each layer, after which the two layers must be bonded together. A double-sided disk requires different stampers for each side, in addition to each layer.

Notwithstanding music, movies and digital photographs, the optical disk is increasingly being used for data storage such as backup and archiving. Instant access to files and the ability to use a built-in DVD player all make the optical disk a superior choice over legacy tape backup units for the average computer user.

A blank optical disk can be purchased in many formats. The least expensive will be an audio CD, as these are single-sided, single layered, and not rewritable. DVDs are more expensive, with a double-sided, double-layered optical disk being the most expensive. Before purchasing this type of optical disk, be sure that your DVD player can handle the format. Blank disks are available nearly everywhere music, DVD movies and computers are sold, including discount department stores.