Re: [Solar-general] Re: [M-Colab] ¿Agregar unrar-free?

Mie Ago 15 05:45:42 CEST 2007

On 8/14/07, Diego Saravia <dsa at unsa.edu.ar> wrote:
> aunque los guardes bien se descomponen, mas de 10 años no duran

Los CDs (CD-R) mas viejos que tengo son del 96-97, y por suerte aun se leen :)
Pero lo que me pase a mi es anecdotico, por eso te paso este
documento, donde citan al instituto de estandares de USA que han hecho
pruebas en camaras donde simulan el paso del tiempo, para hacer luego
recomendaciones para las bibliotecas y oficinas del gobierno que
guardan datos en CDs:
http://www.clir.org/PUBS/reports/pub121/sec4.html
En resumen, depende mucho de la calidad del disco (no vas a comparar
esos sin nombre que te venden de a 1000 en "la casa del cd virgen" con
un Yamaha Gold que viene en caja individual) y de como lo guardes y
como lo trates:

So what is the life expectancy of a disc? First, we must define life
expectancy. For most users, it means the length of time for which the
disc remains usable. But that implies some acceptable amount of
degradation. How much and what type of degradation is acceptable?

With CDs and DVDs, the user does not notice early degradation because
the error detection and correction capability built into the system
corrects a certain number of errors. The user notices a problem only
when the error correction coding is unable to fully correct the
errors.

One method for determining end of life for a disc is based on the
number of errors on a disc before the error correction occurs. The
chance of disc failure increases with the number of errors, but it is
impossible to define the number of errors in a disc that will
absolutely cause a performance problem (minor or catastrophic) because
it depends on the number of errors left, after error correction, and
their distribution within the data. When the number of errors (before
error correction) on a disc increases to a certain level, the chance
of disc failure, even if small, can be deemed unacceptable and thus
signal the disc's end of life.

Manufacturers tend to use this premise to estimate media longevity.
They test discs by using accelerated aging methodologies with
controlled extreme temperature and humidity influences over a
relatively short period of time. However, it is not always clear how a
manufacturer interprets its measurements for determining a disc's end
of life. Among the manufacturers that have done testing, there is
consensus that, under recommended storage conditions, CD-R, DVD-R, and
DVD+R discs should have a life expectancy of 100 to 200 years or more;
CD-RW, DVD-RW, DVD+RW, and DVD-RAM discs should have a life expectancy
of 25 years or more. Little information is available for CD-ROM and
DVD-ROM discs (including audio and video), resulting in an increased
level of uncertainty for their life expectancy. Expectations vary from
20 to 100 years for these discs.

Few, if any, life expectancy reports for these discs have been
published by independent laboratories. An accelerated aging study at
NIST estimated the life expectancy of one type of DVD-R for authoring
disc to be 30 years if stored at 25°C (77°F) and 50% relative
humidity. This testing for R discs is in the preliminary stages, and
much more needs to be done.

> por ejemplo las bacterias se los comen, peor si hay humedad

Existe solo un hongo que puede comer una de las capas de un CD, y está
en Belice. Al menos ahi ese hongo naturalmente infecta los CDs. Quizas
haya bacterias que si las pones en cantidad suficiente sobre un CD te
lo estropean, pero no conozco que bajo condiciones normales de
almacenamiento haya bacterias que usen CDs como sustrato de
crecimiento.

-- 
Sebastián Bassi (セバスティアン)
Diplomado en Ciencia y Tecnología.
GPG Fingerprint: 9470 0980 620D ABFC BE63 A4A4 A3DE C97D 8422 D43D