halt and catch fire (HCF)

programmingops culture

A jokingly named machine instruction said to make a CPU seize up - and, on some chips, a real undocumented opcode that does.

HCF began as programmer humor for an instruction that would do something catastrophic like set the processor on fire, but the Motorola 6800 really had undocumented opcodes that locked the CPU into a runaway read cycle, and the nickname stuck to them. The name is folklore; the lock-up behavior on those chips is real.

Disputed / commonly mistold A popular version of this story is inaccurate - see the note above.

Also known as: HCF, halt and catch fire

← All glossary entries