我在MSDOS中想用msd命令察看系统信息，输入msd后，为什么显示如下的提示：
C:\>msd
'msd' is not recognized as an internal or external command,
operable program or batch file.
C:\>
另外还有好多命令在我的MSDOS里都是这样提示的，比如，lh命令，老是显示：C:\>lh
'lh' is not recognized as an internal or external command,
operable program or batch file.
C:\>
还有memmaker命令，
C:\>memmaker
'memmaker' is not recognized as an internal or external command,
operable program or batch file.
C:\>
郁闷，还有好几个这命令都是样的提示，这到底是怎么回事啊？请教高手！！！！
C:\>msd
'msd' is not recognized as an internal or external command,
operable program or batch file.
C:\>
另外还有好多命令在我的MSDOS里都是这样提示的，比如，lh命令，老是显示：C:\>lh
'lh' is not recognized as an internal or external command,
operable program or batch file.
C:\>
还有memmaker命令，
C:\>memmaker
'memmaker' is not recognized as an internal or external command,
operable program or batch file.
C:\>
郁闷，还有好几个这命令都是样的提示，这到底是怎么回事啊？请教高手！！！！