The file pointed to by the index may be another directory. There is one special directory, called the root . It is very nice that directories and file descriptors are separate, and the directories are implemented just like files. In Unix, there is one directory per process, called the working directory, that the system remembers. When it gets a file name, it assumes that the file is in the working directory.
Many systems allow more than one current directory.
This set of directories is called the search path or search list . This is very convenient when working on large systems with many different programmers in different areas. For example, in Unix the shell will automatically check in several places for programs. However, this is built into the shell, not into Unix, so if any other program wants to do the same, it has to rebuild the facilities from scratch. This is yet another example of locality.