10.0867 lifetime of CDs

WILLARD MCCARTY (willard.mccarty@kcl.ac.uk)
Sat, 19 Apr 1997 22:07:15 +0100 (BST)

Humanist Discussion Group, Vol. 10, No. 867.
Center for Electronic Texts in the Humanities (Princeton/Rutgers)
Centre for Computing in the Humanities, King's College London
Information at http://www.princeton.edu/~mccarty/humanist/

[1] From: Han Baltussen <hb62@umail.umd.edu> (29)
Subject: Re: 10.0857 lifetime of CDs

[2] From: "Theodore F. Brunner" <tbrunner@uci.edu> (47)
Subject: Re: 10.0857 lifetime of CDs

Date: Sat, 19 Apr 1997 12:22:32 +0000
From: Han Baltussen <hb62@umail.umd.edu>
Subject: Re: 10.0857 lifetime of CDs

I forwarded the question to a friend of mine (PhD in Physics) who has worked
on CD coatings, and his quick response was as follows:

>it mentioned that music CD's were
>starting to radomize after for or five years rather than the unlimited
>lifespan that was previously thought.
This seems highly unlikely. The read-only CD mainly consists of a
polycarbonate plate (special low-birefringence grade). The information is
encoded in micrometer-sized pits in the surface, which is covered by a thin
gold mirror and a protective coating. Some brands of early read-only CD's
had a limited lifetime due to degradation of the upper two layers (the
mirror and protective coating). This was fixed in newer CD's. The rate of
information loss by deformation of the polycarbonate substrate itself
depends strongly on temperature. As the glass transition temperature of
polycarbonates is high (e.g. 150 C), I would not expect noticable changes at
room temperature in centuries.

> They all say that it is indefinite but then they say that is only for
>commercial CD's that have a glass master.
Those are the conventional read-only CD's discussed above.

>They say the one's you burn
>youself that are dye based or are based on Photo-CD technology degrade when
>exposed to light.
As far as I know Photo-CD's are based on laser-burning of a metal layer. I
don't expect the metal layer to degrade by exposure to ambient light. The
sensitivity to photodegradation of dye-based recordable CD's depends on the
type of dye used. It is hard to make a general remark on this type of
recordable CD's.

hope this is helpful,
Han Baltussen

Date: Fri, 18 Apr 1997 08:39:49 -0700
From: "Theodore F. Brunner" <tbrunner@uci.edu>
Subject: Re: 10.0857 lifetime of CDs

In response to the query about the lifetime of CD ROMs, let me provide the
following information: the TLG Project issued its first CD ROM version (CD
ROM "A") in 1985, followed by a CD ROM "B" in 1986, a "C" version in 1987,
and a "D" version in 1992. Altogether, an aggregate of roughly 6,000 TLG
disks has been in circulation since 1985.

The TLG provides offers free replacement for any CD ROM which ceases to
function without obvious signs of abuse (e.g., severe scratching of
surface, or cracks). Over a twelve-year period, we have received only one
request for replacement of a disk which, though not functioning properly,
lacked obvious signs of abuse (we have received many requests for CD ROMs
that _had_ clearly been mishandled).

I have personally checked several copies of our first (1985) generation of
CD ROMs this morning; all of them function flawlessly.

Ted Brunner

Theodore F. Brunner, Director
Thesaurus Linguae Graecae
University of California Irvine, Irvine CA 92697-5550
Phone: (714) 824-6404
FAX: (714) 824-8434
E-mail: tbrunner@uci.edu
TLG Home Page: http://www.uci.edu:80/~tlg/