operating system shell for DOS operating systems

- responsible for setting up the system by running the AUTOEXEC.BAT
- COMMAND.COM are DOS programs that use the MS-DOS API to communicate with DOS
- batch mode (FOR, IF, GOTO, REM, CALL, :LABEL)
- Redirection (>, >>, <, | &)
- Variables (%VARIABLE%, %0, %1...%9)
* interactive mode is limited to 126 characters.

Internal commands:
COPY, REN
CD, DIR, MD, RD
DEL
SET, TIME, VER, VOL, ECHO, CLS