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>.