Q I recently needed to retrieve copies of diagrams that I created over ten years ago. I keep an old G5 running Mac OS X 10.4.11 with Classic for this purpose, but when I tried to access the Claris Draw and Photoshop files, I discovered that their icons were blank and double-clicking them did not open them up in an application. This was not helped by rebuilding the Classic Desktop either. Thankfully I found copies on the Mac’s second hard disk, where they were shown correctly, but copying those over to the primary disk does not fix the problem. What has gone wrong?

A When problems like this occur in the Classic environment, they are almost always due to an error in the hidden Desktop database files. Rebuilding them through the Classic pane should clear the problem, but sometimes does not, for example when the disk is running short of space, or ‘bit rot’ has set in.

The latter is an inevitable slow degradation in data storage such as hard disks that leads to accumulated minor errors. Of course in OS X this type of problem is not associated with any Desktop database, but because of a breakdown in association between Finder file types, icons, and applications; you should be able to fix that in the Finder’s Get Info dialog.

Comments You should be concerned about the long-term consequences of bit rot, which puts these old files at risk of being lost forever. It would also be very serious if one day your G5 went west, taking its hard disk with it. Inaccessible file formats are best converted to more modern types such as EPSF or PDF and saved to archival-quality optical disk storage.

Updated from the original, which was first published in MacUser volume 26 issue 11, 2010.