My program won't run from the C:\ prompt!
When you install DOS on your system, by default, the program files for external commands are written to a directory named DOS on the drive letter that your computer boots from. Because most systems boot from drive C, most of the time you'll find that the DOS directory is called C:\DOS.
If you look into the AUTOEXEC.BAT file, you'll probably find a command line that begins with PATH, followed by a list of directories. This command tells DOS where to search for program files when it is trying to run a command. If your DOS directory is listed in the PATH command line, COMMAND.COM can find the program files for external commands no matter what disk drive or directory you are logged on to. A PATH statement looks like this:
Path=c:\; c:\DOS; c:\windows
If you install a program to a new directory without adding that directory to the PATH statement, that program will run only if you change directories to where it resides. When you add the program's home directory to the PATH statement, you can execute any file in that directory, no matter what directory you are currently in.