Halt and Catch Fire

The term "Halt and Catch Fire" (HCF), often associated with the mnemonic HCF, refers to a machine code instruction that causes a computer's central processing unit (CPU) to enter a state of non-meaningful operation, typically necessitating a system restart. While initially a humorous, fictitious concept in the context of IBM System/360 computers, HCF evolved to describe real, often unintentional, CPU behaviors caused by specific instruction sequences or hardware design flaws. These behaviors effectively freeze the processor, rendering the system unresponsive until a reset. Although the name facetiously suggests the CPU would overheat and burn, the reality is a system lock-up due to continuous, unrecoverable states.