Most of the time you work with files, they are stored on your
computer's hard disk and are accessible using the file and directory
handling commands discussed in
``Working with files and directories''.
However, it may be necessary to use other types of storage device.
For example, you might want to pass a copy to the user of another
machine not connected to your own, or to store infrequently used
material, or to make a backup copy of your work. This chapter
explains how to use: