It is not technically correct to say that a window displays the contents of a file , rather that each window displays the contents of a buffer . A buffer is an object that contains data from the point of view of the editor, whereas a file contains data from the point of view of the operating system. A buffer is a temporary storage area used by the editor to hold the contents of a file while the process of editing is taking place. When editing has finished the contents of the buffer can then be written to the appropriate file. When the user exits from the editor, no information concerning buffers or windows is saved.
A buffer is often displayed in its own window, although it is also possible for many buffers to be associated with a single window, and for a single buffer to be displayed in more than one window.
In most cases, there is one buffer for each file that is accessed, but sometimes there is more than one buffer for a single file. There are also some buffers (such as the Echo Area, which is used to communicate with the user) that are not necessarily associated with any file.