That would be DOS 3.x. You could specify a file under (Apple's) DOS with "long_filename,S6,D1". File names could have up to 33 chars and had type information (one byte) so as not to rely on naming conventions.
My 33 figure was wrong (either me or Wikipedia). Maybe the directory entry had 33 bytes (30 for the file name, 1 for type, and two for track and sector)
