Is there a maximum character length rule for a filename?

Hi all,

Ive just noticed that my Adobe Image Ready only allows me to save files names of 27characters in length or less.

Is there a general character length rule in working with filenames. I know windows doesnt have a problem what about other OS? Apple etc.?

Im just trying to put really descriptive names in some of my files wokring with flash and photoshop/imageready etc.

Any help would be great.