### 20.2.1 The Directory File ‘`dir`’

For Info to work, the ‘`info`’ directory must contain a file that serves as a top level directory for the Info system. By convention, this file is called ‘`dir`’. (You can find the location of this file within Emacs by typing `C-h i` to enter Info and then typing `C-x C-f` to see the pathname to the ‘`info`’ directory.)

The ‘`dir`’ file is itself an Info file. It contains the top level menu for all the Info files in the system. The menu looks like this:

    * Menu:
    * Info:    (info).     Documentation browsing system.
    * Emacs:   (emacs).    The extensible, self-documenting
                           text editor.
    * Texinfo: (texinfo).  With one source file, make
                           either a printed manual using
                           @TeX{} or an Info file.
    …

Each of these menu entries points to the ‘Top’ node of the Info file that is named in parentheses. (The menu entry does not need to specify the ‘Top’ node, since Info goes to the ‘Top’ node if no node name is mentioned. See Nodes in Other Info Files.)

Thus, the ‘`Info`’ entry points to the ‘Top’ node of the ‘`info`’ file and the ‘`Emacs`’ entry points to the ‘Top’ node of the ‘`emacs`’ file.

In each of the Info files, the ‘Up’ pointer of the ‘Top’ node refers back to the `dir` file. For example, the line for the ‘Top’ node of the Emacs manual looks like this in Info:

    File: emacs  Node: Top, Up: (DIR), Next: Distrib

In this case, the ‘`dir`’ file name is written in upper case letters—it can be written in either upper or lower case. This is not true in general, it is a special case for ‘`dir`’.