On: Mon, 03 May 1999 12:59:34
"John A. Lind" <jlind@xxxxxxxxxxx> wrote
>This hit on the problem exactly although I didn't cite it in the original
>posting. One of the decennial census archives (1960?) was nearly
>completely lost by the U.S. Government Census Bureau for this very reason.
>It had not been transferred as "legacy data" into a newer system.
>Fortunately it was caught just before the hardware (tape drives?) and
>software used to read it was completely "sundown."
I set up a 20-year archive in the late 70's which would require periodic
copying. To recover the data you still have to have hardware capable of
reading the tape. However, some people have made the mistake of writing
to the tape in a "disk image" format. That requires that you have also
have the original model hard drive as well. A no-no.
>... In addition, there could also be degradation moving an image into a >new
>format. To wit, try saving a "jpg" image as a "BMP" or some other >format.
>Between certain formats information is lost due to the >differences.
The information is not lost due to the conversion from one format to
another but rather due to the choice of format. "jpg" (or JPEG, Joint
Photagraphic Experts Group) is a "lossy" compression method. The amount
of information lost during the compression depends on the compression
ratio selected. There are also "lossless" compression methods. The
method you choose depends on what you're trying to achieve. In
archiving something of great importance one would choose little or no
compression but pay the price in increased storage costs.
Chuck Norcutt
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