optical disk

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Related to optical disk: optical disc, magnetic disk

optical disk,

any of a variety of information storage disks that are played or read using a laserlaser
[acronym for light amplification by stimulated emission of radiation], device for the creation, amplification, and transmission of a narrow, intense beam of coherent light. The laser is sometimes referred to as an optical maser.
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. Optical disks include compact discscompact disc
(CD), a small plastic disc used for the storage of digital data. As originally developed for audio systems, the sound signal is sampled at a rate of 44,100 times a second, then each sample is measured and digitally encoded on the 4 3-4 in (12 cm) disc as a series of
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 (CDs and CD-ROMs), laser discs (see videodiscvideodisc
or videodisk,
disk used with a special player and television to reproduce both pictures and sound. A videodisc player cannot record television programs off the air for later playback, unlike a videocassette recorder (VCR) or recordable DVD (see digital
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), and digital versatile discsdigital versatile disc
or digital video disc
(DVD), a small plastic disc used for the storage of digital data. The successor media to the compact disc (CD), a DVD can have more than 100 times the storage capacity of a CD.
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 (or digital video discs; DVDs and DVD-ROMs). WORM [Write Once/Read Many] disks can be used to record data, but once data is recorded it cannot be altered except by obliterating the old version and storing the new version on a previously unused portion of the disk. Magneto-optical disks, such as the rewritable optical disk and the recordable disk used with the Mini Disc player, have a special layer, as of barium ferrite, that can be magnetically polarized by a recording head when heated with a laser. Data or sound may be recorded to and erased from any portion of a magneto-optical disk multiple times.
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optical disk

[′äp·tə·kəl ′disk]
(computer science)
A type of video disk storage device consisting of a pressed disk with a spiral groove at the bottom of which are submicrometer-sized depressions that are sensed by a laser beam.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

optical disc

A direct access storage device that is written and read by light. The most common types are CD, DVD and Blu-ray. As removable media, optical discs superseded the earlier magnetic disk cartridges because they weigh less, have higher capacities and are not subject to head crashes or corruption from stray magnetic fields. Optical media also have a 30-year life and are less vulnerable to extreme hot or cold.

However, as a transportable storage medium, they have mostly been superseded by USB-based flash drives and external hard drives. Following are the major categories of optical discs in order of writability.

Read-Only (Factory Pressed)
Read-only discs are pressed from a master at the time of manufacture and cannot be erased. They include the music CD, CD-ROM, DVD-ROM, DVD-Video and BD-ROM (Blu-ray). See CD, DVD and Blu-ray.

Write-Once (Burnable)
Write-once discs are recorded in the user's environment but cannot be erased. They include CD-R, DVD-R, DVD+R, BD-R (Blu-ray) and WORM discs, as well as magneto-optic (MO) and ultra density optical (UDO) discs in WORM mode. See magneto-optic disk and UDO.

Rewritable (Phase Change and Magneto Optic)
Rewritable discs 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 (Blu-ray) as well as ultra density optical (UDO). See phase change disc.

Magneto-optic (MO) disks combine optical and magnetic technologies (see magneto-optic disk). See ISO/IEC 13346, multilevel optical disc, holographic storage, WORM and legality of optical storage.

Writability  Optical Disc Types

    Read only    CD, CD-ROM
                 DVD-ROM, DVD-Video

    Write once   CR-R
                 DVD-R, DVD+R
                 BD-R, WORM

    Rewritable   CD-RW
                 DVD-RW, DVD+RW

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Better microreplication in injection molding of optical disk substrates could be predicted for the blends with decreasing glass transition temperatures as demonstrated in the following section.
MCS will produce the latest multimedia compact optical disks at an existing 20,000sq ft business unit at the Ynyscedwyn Enterprise Park, Ystradgynlais, as part of a pounds 7.4m investment.
Optical disk systems are commonly used by organizations such as financial institutions, insurance companies, engineering firms, publishing companies, hospitals, and government agencies.
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The converted image then is stored on optical disks.
Such devices work like a traditional jukebox, storing many optical disks that can be called up one at a time as needed.
The image is then sent to the computer as a series of dots, commonly referred to as a "bitmap." This image is then compressed and stored to an optical disk.
The enthusiasm is less for the optical disk medium itself than for its integration with a software package that allows patient files to be retrieved in seconds, rather than hours or days as is the case with such traditional archiving tools as microfiche, magnetic tape, and paper.
With an optical-disk jukebox system, the data can be downloaded from the computer to an optical disk overnight, freeing the expensive hard disk storage of the main computer for daily transactions.
The voluminous patient records, reports, and tests which we once stored on paper are now kept on optical disk. Up to seven years of files are maintained for each patient and can be easily accessed when needed at the push of a button.
But all three programs can be stored on a single CD-ROM disk, which employs optical disk technology.
Both she and Mueller include comparisons of rewritable optical disk technology with CD-ROM, WORM, and magnetic storage.