A system of organizing files in an operating system in which all files are stored in a single directory. In contrast to a hierarchical file system, in which there are directories and subdirectories and different files can have the same name as long as they are stored in different directories, in a flat file system every file must have a different name because there is only one list of files. Early versions of the Macintosh and DOS operating systems used a flat file system. Today's commercial operating systems use a hierarchical file system.
Flat file system should not be confused with flat file.
