Inexplicably decaying data
By Charles Miller

Once when I bought a new set of tires for my car I noticed the workers taking my “brand-new” spare and replacing it with one of my old tires. I objected vociferously, telling them the spare had never even been on the ground.

The store owner explained that one of my two-year-old, almost-worn-out tires was a safer spare than my 10-year-old, never-used spare because of something called “dry rot.”

That experience prepared me for my first encounter, years later, with a new techie colloquialism. A client was encountering difficulty reading data from a collection of old floppy disks. The disks had been properly stored, but some could not be read. There was no reason that some disks that had never been used or disturbed should not be in the same condition as when they were created. This problem is caused by what we in the profession call “bitrot.”

Bitrot is a somewhat whimsical term that describes the phenomenon of spontaneous electronic data decay that lacks any readily identifiable cause. Sometimes bitrot refers to the physical decay of a storage medium (more on that later).

Far too many computer users have had the experience of saving important files or pictures to some electronic storage medium for safekeeping only to find, months or years later, the data on these undisturbed disks cannot be accessed.

How can such a thing happen? The disk or memory stick containing the important data had been properly stored and might even have been accessed in the recent past without difficulty. There is no easy way to explain why data corruption occurs even though the data simply sat in storage. This is bitrot.

There is no point in whining, “But the disks were okay yesterday!” The fact that a disk was okay at one time has absolutely no bearing on whether its condition will be unchanged in the future.

Explanations for what causes bitrot run the gamut and experts have not agreed. Some say cosmic rays are responsible (a proven hazard for satellites in earth orbit). Others point out that the earth’s magnetic field constantly acts on all forms of electronic storage media and there is no escaping it, except in space (see previous sentence). Still others believe it is the nature of electrically charged data to fade away over a period of years.

Regardless of the type of storage medium, all types have their problems. Old-style paper punch cards are subject to becoming brittle with age. Floppy disks and magnetic tape degrade as bits lose magnetic orientation. Optical discs such as CDs and DVDs are immune to this, but the breakdown of the plastics and resins used to make the disks are the cause of their bitrot.

All of this brings us to the question of what are we to do for archival storage in the electronic age. Of all computer-based storage options, probably the best for now is the CD or DVD. In some jurisdictions courts have recognized these as legally equivalent to microfilm.

Store your disks in a cool, dry place with consistent temperature and relative humidity. Store disks in their plastic jewel cases, not paper sleeves. Some studies indicate the acids in paper contribute to CD bitrot, so you might think about taking all the paper jackets out of your music CD collection.

Finally, for really important data, keep more than one copy.

Charles Miller is a freelance computer consultant, a frequent visitor to San Miguel since 1981 and now practically a full-time resident. He may be contacted at 044-415-101-8528 or email FAQ8@SMAguru.com.