Frequently Asked Questions About Optical Media
- How is information recorded onto optical media?
- What issues are associated with the stability of optical
This set of Frequently Asked Questions provides a brief overview of optical media from a records management perspective. This is an evolving area, and we will post additional answers as they are developed. Please bookmark this page to monitor progress.
Also, please review Frequently Asked Questions about Imaged Records and Frequently Asked Questions (FAQs) about Optical Storage Media: Storing Temporary Records on CDs and DVDs for additional information.
How is information recorded onto optical media?
Information is recorded as microscopic areas of reflective differences in a layer attached to the substrate of the optical recording media. These reflections can be detected by a laser, and then "read" by application software. Optical media employ a variety of recording technologies.
What issues are associated with the stability of optical media?
From a broad perspective, the following interrelated issues affect the stability of optical media:
- physical stability of optical media
- data stability of information recorded on optical
- technological stability of optical media
Of these three inter-related issues, physical stability and data stability are less problematic than technological stability. Economic issues also apply overall, such as how long the software vendor has been in business, since most optical media is proprietary. Due to their proprietary nature, optical media are also susceptible to sales and marketing decisions, such as where the products are advertised or which integrators work with the products, which should be considered when deciding whether to use optical media, as well.
The physical stability of optical storage media is affected by environmental factors involving where the media is used and where the media is stored. The factors include:
Humidity and temperature
- The humidity and temperature determine the amount of water that comes into
contact with the media. Contact with humidity or water can either cause the
binding agent (glue) used in the media to break down or alter the reflectivity
of the (semi) metallic coating into which the data are etched. Either
situation could affect data retrieval.
- While the effect of humidity and temperature conditions varies among types and brands of optical storage media, a generally accepted, recommended temperature/humidity range is 68ºdeg;F (max. variation ± 1ºdeg;/day, ± 3ºdeg;/year) and 40% relative humidity (max. variation ± 5%/day, ± 5%/year). As there are no national or international temperature or humidity standards for the storage of optical media, consult the manufacturer's environmental storage specifications for specific media.
- Inappropriate use or storage of optical media can cause warping of an optical disk or scratching of the polycarbonate substrate. Either situation could affect the ability of the laser to read/write information to or from the disk.
Dust and dirt
- Dust and dirt, whether present during use or in the storage area, can contaminate the media and adversely affect the physical stability of the media or cause read/write errors, which would also affect the data stability of information stored on the disk.
Light and magnetism
- For re-writable optical media, such as phase-change or magneto-optical storage, exposure of the media to light or magnetism could alter the recorded information.
These factors that relate to physical stability have been derived from accelerated aging experiments in which data are read/written to and from storage media under various environmental conditions. Useful media life is determined by measuring the number of errors (also known as "block error rates" or BLERs) for a particular medium over time, below a maximum acceptable level of read/write errors. On the basis of these types of experiments, manufacturers have claimed that the lifespan of optical media ranges from 15 to 200 years. Generally, manufacturers cite longer life spans for recorded versions versus unrecorded (i.e., blank) versions of particular optical media formats, so order media as you need it and don't stockpile inventories of unused media. Note that deterioration begins at the time of manufacture, not recording.
Data stability factors
The stability of information recorded on optical media is closely linked to the physical stability of the media. Unless the physical stability is ensured, the data stability will be endangered. The only way you can measure physical stability is by measuring errors and monitoring data stability.
All optical storage media technology have built-in error detection and correction capabilities. The error recovery capabilities and tolerances of various optical media differ. Utilities that monitor the number of BLERs (block error rates) on optical media are used to determine its stability characteristics and migration or recopying intervals.
Technological stability factors
Technological stability of optical media is affected both by the longevity and standardization of hardware and software. When choosing to use optical media, assess the technological factors, which include:
Longevity/standardization of hardware
- Compatibility of an optical medium across equipment produced by different
- Availability of equipment necessary to read a particular optical medium
- Adherence of diverse read/write optical media hardware to various computing interface standards (e.g., SCSI (small computer system interface) from the ANSI family of standards for personal computer peripherals) that allow your computer to interact with peripheral devices (such as printers, CD-ROM drives, etc.)
Longevity/standardization of software factors
- Persistence of optical media logical file formats (i.e., how long until
the file formats become obsolete)
- Integration/maintenance of interface of optical media with various
- Media indexing schemes
The technological stability of optical media could be impacted by technological obsolescence. In addition, marketing factors, such as current and anticipated market share or the marketability of particular hardware and software products, may also affect the viability of particular products for long term storage of information.
Updated 08/06/07Top of Page