Specifications

These filenames are valid because none of them are too long,
and only legal characters have been used. The following are
examples of illegal filenames, along with an explanation:
3RDQUARTER.SALES
This is too long. MS-DOS will accept this filename, but it
will be shortened to fit the size limits. The altered filename
would read 3RDQUART.SAL. As you can see, both the
filename and its extension have been shortened to the legal
length.
CHAPTER/4
The slash ( / ) is an illegal filename character. MS-DOS
will reject the filename and ask for another.
NEW EMPL.LTR
This would be rejected by MS-DOS because of the space in
the filename.
Certain filename extensions have been set aside so that MS-DOS
can recognize program files. These are:
COM
(for COMMAND file)
EXE
(for EXECUTABLE file)
BAT (for BATCH file)
Program files should always have one of these three filename
extensions. Data files should never use these reserved
extensions. They can, however, use any other extension.
Filename extensions are optional with data files, so you can
leave them off entirely, if you want. Using filename extensions
with data files allows you to have many different variations for
a set of filenames. For instance, different chapters of a book
might be named:
4-22 Using MS-DOS With Your Computer