Just as a bit of lesser-known information on OS X I thought that I’d give a quick listing of some of the hidden files on all Mac OS X storage devices (this includes the internal/ boot disk, any external hard drive, any flash drive, any digital camera, and any iPod as long as they are formatted for OS X).
.DS_Store: (is actually in every folder) the file that stores data needed by Finder. .fseventsd: I think this was new in 10.5. It is an always-up-to-date database of the filesystem. This file is what Time Machine uses to know what has changed since the last backup. .Spotlight-V100: Spotlight’s index. This will be on storage devices for which you’ve disabled Spotlight as well as those that are searchable. .Trashes: The trash for that storage device.
The “.” at the start of each name is what tells Finder to hide them (unless you have the right preference set in com.apple.Finder.plist). Many more hidden files also reside on your internal/ boot disk and your Time Machine backup disk, but I just listed the ones that are on every Mac OS X storage device. Enjoy, Alex.