In the physical world (3space, meat-space), entropy is the unavoidable consequence of the 2nd law of thermodynamics. In theory the 2nd law doesn't hold in cyberspace, but in practice it does. Information that's stored in computers "rusts" at least as fast as information stored in real-world media. I'm reminded of this every time I walk through the cemetary down the street from my house: many headstones manufactured in the 17th century still convey the information that they did when they were new. On the other hand, when my Mom "upgraded" to Windows '95 a few years back she found that all of the documents she had written in her low-end microsoft word processor were completely illegible on the new version of the high-end office suite, even though only 5 years had passed. She was lucky to be computer-naive - she lost nothing since she had printed all of the documents on paper.

What can you do? To start with, be aware of information entropy, and decide whether or not you care about it. If you don't care then you're wasting your time reading this document; if you do then I hope that you'll learn something from it.

In my (admittedly brief) experience with computers, data becomes inaccessible for two reasons: the physical media that it's stored on becomes unreadable, or the format that the data is stored in becomes indecipherable.

Media:

• cassette tape
• 8-inch floppy
• MO cartridge disk
• 1/4 cartridge tape
• 5 1/4-inch floppy (CP/M, Apple ][, trs-80, C64, PC)
• 4MM DAT/DDS
• 3 1/2-inch floppy
• CDROM

Media can become unreadable if the media itself fails (magnets, scratches) or if the reader breaks and can't be fixed.

• Time/Date
• Country Codes, Currencies
• Addresses (vCard/iCard)
• other data: http://www.w3.org/TR/xmlschema-0/

-- TobyCabot - 22 Feb 2002