It is a set of instructions, written in language the computer understands, that defines how your computer will operate. It makes it possible for you as the user to communicate with the disk drives, the processor, the printer, and any other hardware you may have. MS-DOS loads some commands into memory when you start your computer.
Internal commands are the more commonly used commands.
Other commands are stored in files and transferred to memory as they are used. These commands are external commands and sometimes perform in ways similar to programs. External commands are listed when you use DIR to view the files on a system disk or directory. Provides online information about the MS-DOS version 5.0 and 6.0 commands. To display help about a particular command, type HELP followed by the command.