资料来源 : Free On-Line Dictionary of Computing

meta bit
     
        The top bit of an 8-bit character, which is on in character
        values 128--255.  Also called {high bit}, {alt bit}, or
        {hobbit}.  Some terminals and consoles (see {space-cadet
        keyboard}) have a META shift key.  Others (including,
        *mirabile dictu*, keyboards on IBM PC-class machines) have an
        ALT key.  See also {bucky bits}.
     
        Historical note: although in modern usage shaped by a universe
        of 8-bit bytes the meta bit is invariably {hex} 80 ({octal}
        0200), things were different on earlier machines with 36 bit
        words and 9-bit bytes.  The MIT and Stanford keyboards (see
        {space-cadet keyboard}) generated hex 100 (octal 400) from
        their meta keys.
     
        [{Jargon File}]