Question
What is an external and internal command?
Answer
In MS-DOS there are two ways commands are executed. An Internal command, which is
a command embedded into the command.com file, and an external command, which is
not embedded into command.com and therefore requires a separate file to be used.
For example, if your computer does not have fdisk.exe and you try using the fdisk
command, you would receive an error "Bad command or file name." Fdisk is an external
command that will only work if fdisk.exe, or in some cases, fdisk.com, is present.
However, as long as MS-DOS is running on your computer internal commands such as
the cd (change directory) command will always be available and does not require any
other files to run.
source:- http://www.computerhope.com/issues/ch000011.htm
