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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5556