The commands that are directly executed by the shell are known as internal commands. No separate process is there to run these commands.The commands that are executed by the kernel are knows as external commands. Each command has its unique process idInternal commands are commands that are already loaded in the system. They can be executed any time and are independent. On the other hand, external commands are loaded when the user requests for them. Internal commands don’t require a separate process to execute them. External commands will have an individual process. Internal commands are a part of the shell while external commands require a Path. If the files for the command are not present in the path, the external command won’t execute.  

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All the internal commands are stored in the file COMMAND.COM whereas all the external commands are stored as individual files in the secondary storage device of the computer system.