HCF /H-C-F/ n.
Mnemonic for `Halt and Catch Fire', any of several
undocumented and semi-mythical machine instructions with
destructive side-effects, supposedly included for test purposes
on several well-known architectures going as far back as the IBM
360. The MC6800 microprocessor was the first for which an HCF
opcode became widely known. This instruction caused the processor
to toggle a subset of the bus lines
as rapidly as it could; in some configurations this could
actually cause lines to burn up. Compare killer poke.