DOS commands are of two types: Internal and External
These commands do not require any special files for being executed and are brought into the computer's memory as soon as the computer is switched on. For example, COPY, DEL, DIR, TYPE, CD, MD, CLS, DATE, TIME and PATH.
These commands require certain special DOS files to get executed. For example, FORMAT, CHKDSK, XCOPY, PRINT, ATIRIB, DISKCOPY, etc. You may not necessarily have all these files in your system. While copying these files onto your system, you must take care that they are of the same DOS version which is installed in your system. Otherwise, you may face problems. For instance, messages like, Incorrect version may appear on your screen if the DOS version is different from the copied file version.