Command Extension are automatically enabled in Windows NT. You can alter this behavior of the command enterpreter with the following switches:

CMD /y      Disable extensions to the Windows NT version of CMD.EXE
CMD /x      Enable extensions to the Windows NT version of CMD.EXE

You may also edit:

HKEY_CURRENT_USER\Software\Microsoft\Command Processor\EnableExtensions

Setting this REG_DWORD value to 0 disables Command Extensions for all CMD.EXE sessions (a 1 enables them).

The command extensions involve changes and/or additions to the following commands:

 
DEL or ERASE
COLOR
CD or CHDIR
MD or MKDIR
PROMPT
PUSHD
POPD
SET
SETLOCAL
ENDLOCAL
IF
FOR
CALL
SHIFT
GOTO
START (also includes changes to external command invocation)
ASSOC
FTYPE
To get the details, type HELP <CommandName>.