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, like this:

DATA.TXT

Do not use uppercase and lowercase letters to distinguish between files. MS-DOS does not recognize the difference and displays all filenames in uppercase.

Some application programs automatically add extensions to the files you create. These programs use the extension to determine whether a data file is compatible. Avoid using the same extensions that your application programs use.

MS-DOS reserves certain filenames for its own use. The reserved filenames are:

AUX

COM4

LPT3

CLOCK$

CON

LST

COM1

LPT1

NUL

COM2

LPT2

PRN

COM3

 

 

MS-DOS also reserves certain extensions for program files. The reserved extensions are .COM, .EXE, and .BAT, and files with these extensions are also sometimes called executable files. Do not use these reserved filenames and extensions for your data files.

The extension .BAT denotes a type of executable file called a batch file. You can use batch files to automate sequences of MS-DOS commands. Even if you are not a programmer, you may want to create some batch files to save time. See “Creating an AUTOEXEC.BAT File” in this chapter for a description of a particularly useful kind of batch file, an autoexecute batch file.

4-10 Using MS-DOS with Your Equity 386SX