EXPAND--Notes

Retrieving files from the Setup disks

Most of the files on the Setup disks provided with MS-DOS 6.22 are
compressed. Each of these compressed files has a file extension that ends   
with an underscore character (_). When you installed MS-DOS, you ran the
Setup program, which expanded these files before copying them to your
system. However, if you need to retrieve just one or a few files from the
original disks, you can use the EXPAND command.

Letting EXPAND prompt you

If you don't include the destination, or don't include the compressed file
and the destination, EXPAND prompts you for the information and provides
examples.