CD-rom longevity

Rab Jackson <pr258rj [at] admin__nls__uk> wrote

>I have had a request from a colleague who is concerned about the
>longevity of CD ROM.

The following appeared on museum-l and is reproduced here without
the knowledge or consent of the author.

    Date: 28 Dec 94
    From: Greg Trimper <administrator_at_cantor-la-1 [at] cantor__com>

    Alex Barker <abarker [at] SUN__CIS__SMU__EDU> writes:

    >I know this may open a can of worms, but have studies been done
    >establishing the archival permanence (or lack thereof) of
    >CD-ROMs?

    There have been several good pointers, including the current
    article on Digital media in the Jan 85 "Scientific American."
    What has been lacking is a practical observation--the 15 year
    quoted average life for CD media is for *manufactured* CD media.
    If an institution is planning on producing its own CDROMs using
    CD-R (recordable) media, the life expectancy is MUCH lower.
    Simple explanation--manufactured CDs use cuts/"pits" in a foil
    to represent the bits, while CD-R media uses dyes--the recorder
    heats up and then burns a layer of dye in the CD-R media, to
    fake the "pits."  This dye-based media is more heat and
    environment sensitive than foil-based manufactured CDs.

    And there haven't been any good studies on the life of these
    disks--until recently, CD-R was used for mastering CDROMs that
    were then manufactured. Recently, prices on recorders have made
    it possible for smaller institutions and individuals to buy the
    recorders, and it is now being sold as an archival media.  And
    of course, a museum probably would rather pay to make a single
    disk, instead of mastering and producing a minimum order from a
    CD manufacturer, so CD-R is bound to be attractive.

    My personal experience has been with some CD-R media failing
    after about three years.

    What I would suggest (and I think has been suggested already) is
    if an institution wants to archive data using CD-R technology,
    they should make at LEAST three copies of each disk, and refresh
    those disks every three years to similar or newer media.
    Furthermore, a tape backup using analog recording would be a
    good failsafe backup--what affects the CDROM would hopefully not
    affect the tape.  That tape should be periodically refreshed as
    well.

    With a "multiple-source" plan such as that, it would take a
    major disaster to  lose your data.  (Need I mention that these
    backups should be kept in different sites, apart from each
    other?)

    Greg Trimper
    Technology Consultant

Laura Gorman
Conservation Services
Bishop Museum
808-848-4112
Fax: 808-842-1914

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                   Conservation DistList Instance 9:9
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