What is DOS command in computer operating system

Dos and MS DOS command
        a command is an specific order from a user to the computer operating system an application to perform a service such as



   There are two types of command
Internal command
External command



Internal
         the internal command which command is available in to the memory that are called internal command
Like that
Delete command, time command and other copy and types command

External command
    the external command are not available into the computer memory this symbols mean that command which are used according to the user are called external command

 Format command and text copy command