X-Message-Number: 5556
Subject: Data Storage
Date: Tue, 09 Jan 1996 10:55:31 -0500
From: "Perry E. Metzger" <>

> From: Joseph Strout <>
> Subject: Re: Data storage
> 
> Monochrome film fades too, probably much faster than CD-ROMs degrade, 
> since the information is encoded chemically rather than physically (i.e. 
> by the presence or absence of matter).

Huh?

1) Once you get to a small enough level, "physical" and "chemical" are
   the same thing.
2) CD-ROMs are made from CDs. They decay very nicely. Among other
   things, degradation of the plastic and glues that surround the
   pitted metal surface occur, as well as fun things like
   photodegradation of the surface itself. In addition, one-off CDs
   (CD-Rs) are notoriously subject to photodegradation.
   Some early CDs sold at the beginning of the CD era have
   become useless because of glues decaying or opaquing. Some have
   not. The claim is that most of the manufacturing processes are now
   "fixed". I don't know whether to believe that or not.
3) Properly developed and fixed b&w photographic negatives have a
   *demonstrated* lifetime of at least six or seven decades, and in
   some cases a century or more. Some processes store nicely, some do
   not. Early color film was notorious for decay, but thats another
   story.
4) I have, in the past, routinely used thirty and fourty year old
   microfiche with no noticeable decay other than that from use.

In short, we have pretty good knowledge of how to keep photographic
film of certain types fresh and happy for years. We can be pretty
certain that techniques likely exist to do the same for some kinds of
CDs, but not for recordable ones, and we don't know for sure if
problems will arise in these media thirty years down the line although
we know how to have that not happen for film.

The whole question is always "how much data do you want to store, and
how much are you willing to let it degrade".

For truly long term storage, nothing beats chiseled stone. Slightly
less good is engraved metal plates. Some legal notices produced this
way in Roman times have survived to this day, and many Pharonic
egyptian inscriptions have survived, demonstrating that it is a good
technique. It is, unfortunately, too bulky for all but the lowest
density information.

Surprisingly, paper seems to work very well when it is high quality,
low acid, and kept away from damaging substances like water, damp, and
fire. If we really want to store reasonable amounts of data for on the
order of centuries, I recommend going back to the future. Specially
printed text in special OCR fonts on low acid paper. Special bar codes
that are REALLY BIG and trivial to write scanners for. It is possible
that some sorts of plastic films would work better, but no one really
knows if they stand up to five hundred years of storage. When I say
"specially printed", I don't mean laser printers or other techniques
that are known to produce bad long term results (laser printouts are
often useless after as little as two years) -- I mean actual ink to
paper, preferably inks that have been in common use for centuries
combined with papers that have demonstrated centuries of survival
capability.

Unfortunately, it seems that people want to store lots of "bulky"
information -- video, pictures, vast and bulky records, etc.

Magnetic media have a known bad track record on this. Mag tapes
recorded in the 1950s have in many cases decayed to uselessness. This
is a well known problem. Paper isn't dense enough.

The only possibilities here are:

1) Film, microfilm, and microfiche, and you accept the problems of
   analog media.
2) Put the stuff on multiple redundant machine readable storage media,
   use fiendish and expensive error correcting codes that would not
   normally be used, and read and re-record the information onto the
   most survivable known archival media every couple of years. Do your
   MTBF calculations so that the odds of losing data are lower than
   some level you find acceptable -- presumably, "far better than the
   odds of the patient making it" seems good.

Now, one more possibility exists for us as cryonicists, which is
storing some of our media at liquid nitrogen
temperatures. Unfortunately, survivability of most of these media
during freezing isn't great. Perhaps some experiments are in order,
although I'd say that the stuff that unfortunately handles freezing
the best is stuff like paper and analog or semi-analog films. Who
knows if anyone will have good enough data to reconstruct the
recording formats on other types of media, anyway...

Perry

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