Archives, ZIP files, SIT files, and other compressed files. Files that contain pictures and sounds encoded in computer-readable form. Graphics files on Web pages are usually in GIF or JPEG format.
Video files contain digitized movies.
Any other type of file. Macs are different, too Macintosh files, regardless of what's in them, usually come in two or three chunks, one of which is the data file. Although you don't see the chunks on your own Macintosh, you do see them if you try to upload them to a non-Mac server on the Net. Although the person who names the file usually tries to be consistent and follow the conventions for naming files, file naming isn't a sure thing. In the old days of DOS, filenames always had an extension at the end of as many as three characters, and the period could be used only to separate the extension.