The concept of INTERNAL COMMANDS started back in the DOS days. Essentially it was a command that could be executed from anywhere in folder structure while at the Command Prompt. These commands were loaded in the memory by the Command.com loader that initiated at startup.
That file has been replaced by cmd.exe in Windows NT/2000/XP/2003 and OS/2
DIR
Lists the files in the current directory
CD, CHDIR
Changes the current working directory or displays the current directory.
COPY
Copies one file to another (if the destination file already exists, MS-DOS asks whether to replace it). (See also XCOPY, an external command that could also copy directory trees)
REN, RENAME
Renames a file or directory
DEL, ERASE
Deletes a file. When used on a directory, deletes all files in that directory, but does not recurse or delete the directory itself.
MD, MKDIR
Creates a new directory
RD, RMDIR
Removes an empty directory
VOL
Shows information about a volume
LABEL
Show or change the label of a volume
VERIFY
Enable or disable verification of writing for files
TYPE
Display the content of a file on the console
Other commands
All commands from the interactive mode can be used in batch files; similarly, one can use batch-file commands directly on the COMMAND.COM command line, interactively. Therefore, it is impossible to separate the syntax to "interactive" or "batch" commands.
BREAK
Controls the handling of program interruption with Ctrl+C.
CLS
Clears the screen.
CHCP
Displays or changes the current system code page.
CTTY
Defines the device to use for input and output.
DATE
Set the date of the system.
ECHO
Toggles whether text is displayed (ECHO ON) or not (ECHO OFF). Also displays text on the screen (ECHO text).
LH, LOADHIGH
Loads a program into upper memory.
LOCK
Enables external programs to perform low-level disk access to a volume. (Windows 95/98/Me only)
PATH
Displays or change the value of the PATH environment variable which controls the places where COMMAND.COM will search for executable files.
PAUSE
Halts execution of the program and displays a message asking the user to press any key to continue.
PROMPT
Displays or change the value of the PROMPT environment variable which controls the appearance of the prompt.
SET
Sets the value of an environment variable ; Without arguments, shows all defined environment variables.
TIME
Set the time of the system.
UNLOCK
Disables low-level disk access. (Windows 95/98/Me only)
VER
Displays the version of the operating system.
On the other hand, EXTERNAL COMMANDS are those not initiated by command.com or cmd.exe, and need to have their entire folder path included for the operating system to find and then execute.