(((The following essay was part of a lengthy net discussion about the archival security of stored digital information. It first appeared in the "Mollusca" Internet mailing list. It was brought to my attention by Steve Jackson and is quoted by permission of Pat LaFollette -- bruces)))
There are three separate issues involved in the archiving of digital documents. The first is captured in this quote from Steve Long:
"About 2 years ago I threw away over 100 eight inch floppy disks because could no longer find machines to read them. Fortunately I was able to convert most of the important data to 5.25 inch floppy disks. Now, my computer has 5.25 and 3.5 inch disks but most users are replacing the 5.25 inch with CD-ROM drives and don't have the space in their PC to include all three. In another couple of years, I will have to convert to 3.5 inch or CD- ROM for my information. After that, who knows, but you can almost guarantee that the storage medium will change again."
The physical media changes as storage technology advances. The marketplace requires that there be one or two "universal" formats at any particular time so that electronic products can be distributed. At present these are the 3.5 inch floppy disk and CD-ROM. The new DVD format is physically the same shape as CD-ROM and DVD readers will be "backwards compatible," == able to read CD-ROMs, at least for a while.
But after DVD has reached its planned maximum capacity of about 15Gb, who can guess what will come next?
The second issue is made clear by William Schleihauf.
"...The various media being talked about == tape in particular == has a lifespan of only a few years (and that's not counting the operators playing frisbee with the tapes on the night shift!). Companies *now* are discovering that some tapes created only a few years ago are coming up with i/o errors, and thus the data is lost. The newer cassettes are better, but again, the half-life is measured in years, not decades.
CDROM == guess what == *maybe* a century, on average, or so the forecasting is."
The currently available digital media are not of "archival" quality, unlike (acid free) paper. Perhaps it's just as well that the physical format of the media keeps changing. It forces people to copy their data to new disks every now and then, while the old ones are still readable!
I've read lengthy discussions of the archival properties of CD-ROM disks. Estimates for some CDR (CD- Recordable) media exceed 200 years, twice as long as commercially pressed CDs. But the glass masters from which commercial CDs are pressed might last millennia.
On the other hand, how long are CD readers likely to be around? The first generation of DVD readers will be backwards compatible, but I doubt CD technology in its present form will last as long as the phonograph. (My LPs, and even some 45s and 78s, are still in playable shape, but my turntable died years ago).
But all that kind of misses the point. One of the tasks performed by traditional librarians and archivists is to protect paper from the ravages of time, the elements, insects, fungus, fire, flood, and undergraduates. Paper can last for hundreds of years, but only if it is taken care of. Paper can also turn to dust in days or weeks.
The analogous task for electronic librarians will be to protect their bits, independent of storage method or medium, by periodically transferring them all to whatever appears to be the most secure and accessible storage technology of the time, and by distributing copies of them to as many other widely dispersed locations as possible.
But there does not yet seem to be an established tradition of digital librarianship to shoulder this responsibility and pass it on from one generation to the next. It's very difficult to establish traditions and a commitment to the long term when the technology is in such a state of flux.
Patrick I. LaFollette
Auto-Graphics, Inc., 3201 Temple Ave., Pomona, California