This is a classic tip for those who ran Mac OS 9 and earlier:
The Desktop file is an invisible file found in the main level of your hard disk in Mac OS 9 or earlier. It is the file that keeps track of all the documents and applications that are on your disk. System 7.0 and later versions use the invisible files named Desktop DB and Desktop DF.
Occasionally, your Desktop file may become too large or may become unusable. It is generally a good idea to rebuild your Desktop file once a month or so in Mac OS 9 or earlier.