Show Me Mac® OS X, v10.3 Panther™

Showing or Hiding File Extensions

A file extension is a three-letter suffix at the end of a document's file name that identifies the file type. For Windows operating system users, a file extension determines which application can open a file; the Mac doesn't use it. You might never have seen a document's file extension because your system might be set up to hide it. The file extension for simple text files is “.txt” (pronounced “dot t-x-t”), and many graphic files have the extension “.bmp” or “.jpg”. This means that the full name for a text file named Memo is Memo.txt. If you double-click a document whose file name ends with the three-letter extension “.txt,” Finder automatically opens the document with TextEdit, a word processing application. ...