Epson Apex 20020 - Manual (Page 82)

The extension is optional and can be up to three characters
long. You can use the extension to further identify a file or to
describe what type of file it is, such as a text file or program file.
When you use an extension, separate it from the filename with
a period. For example, an MS-DOS filename might look like
this:
DATA.TXT
Some application programs automatically add extensions to the
files you create. These application programs use the extension
to determine whether it is a compatible data file. Avoid using
the same extensions as your application programs. Also, do not
use uppercase and lowercase letters to distinguish between files.
MS-DOS does not recognize the difference and displays all
filenames in uppercase.
Certain extensions are reserved for program files and you must
not use them for your data files. The reserved extensions are
.COM, .EXE, and .BAT. Files with these extensions are also
sometimes called executable files.
The .BAT extension denotes a particular kind of executable
file called a batch file. Batch files can be used to automate
sequences of MS-DOS instructions. Even if you are not a
programmer, you may want to create some batch files to assist
you in your work. A particularly useful kind of batch file, called
an autoexecute batch file (or “AUTOEXEC” file) is discussed
later in this chapter.
Copying Files
You can use the COPY command to copy individual files or
groups of files. COPY is an internal command; you can use it
any time you see the MS-DOS command prompt.