Tree-Structured Directories

• Once we have seen how to view a two-level directory as a two-level tree, the natural generalization is to extend the directory structure to a tree of arbitrary height ( see Fig. 13).

  Figure 13: Tree-structured directory structure.

  
• This generalization allows users to create their own subdirectories and to organize their files accordingly.
• A tree is the most common directory structure. The tree has a root directory, and every file in the system has a unique path name.
• A directory is simply another file, but it is treated in a special way. All directories have the same internal format.
• One bit in each directory entry defines the entry
  • as a file (0),
  • as a subdirectory (1).
• Path names can be of two types: absolute and relative
  1. An absolute path name begins at the root and follows a path down to the specified file, giving the directory names on the path.
  2. A relative path name defines a path from the current directory.
• With a tree-structured directory system, users can be allowed to access, in addition to their files, the files of other users.
  • For example, user $B$ can access a file of user $A$ by specifying its path names.
  • User $B$ can specify either an absolute or a relative path name.
  • Alternatively, user $B$ can change her current directory to be user $A$'s directory and access the file by its file names.