Meta Bit N. The Top Bit Of An 8-bit Character, Which Is On In Character Values 128-255.

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meta bit n.

The top bit of an 8-bit character, which is
on in character values 128-255. Also called high bit,
alt bit, or (rarely) 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