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Write-once, read-many

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Definitions Edit

A write-once, read-many (WORM) is

a type of optical disk on which information can be recorded only once but from which it can be retrieved and read many times.[1]
[a] data storage format, usually an optical disk, that allows information to be read, but not modified, after it has been recorded.[2]

WORM technologies Edit

WORM optical recording technology processes include ablative, thermal bubble, bimetallic alloy, dye-polymer, and phase change.

  • The ablative process, the earliest commercially available optical recording technology, alters the optical digital data disk's reflective characteristics by creating submicron-sized pits, or bubbles, to indicate 1's and 0's.
  • Thermal bubble recording creates bubbles on the optical media's surface using the laser beam's concentrated energy.
  • Bimetallic technology uses a laser beam to fuse several alloys together into a totally new alloy with a different reflective index.
  • In the dye-polymer and phase change recording technologies, the laser beam alters the media's physical color and reflective characteristics, with the information signified by the color changes.

Because these recording technologies involve a non-reversible physical alteration of the recording surface, they are designated "write once."

When data integrity is a primary concern, WORM optical digital data disks become attractive because the recorded data cannot be altered or erased. If at some point an existing image is determined to be incorrect or is no longer needed, the electronic pointer to that search location can be disabled. This pointer disabling process effectively eliminates future user access. New or corrected data is then written to a different, unused area of the optical digital data disk. This process is essentially transparent to the user. Although access to the original image is blocked, the data is still on the WORM disk and potentially remains accessible unless expressly overwritten by the system manager to obliterate the recorded data pattern.

One of the most recent developments in write-once, read-many optical digital data disks is the emergence of compact disc recordable or CD-R.

References Edit

  1. EPA, Vocabulary Catalog List Detail - Records Glossary (full-text).
  2. Society of American Archivists, Glossary of Archival and Records Terminology (full-text).

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