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Halt and Catch Fire (HCF) is a type of machine language instruction that would cause the computer to cease operations. It began as a purely theoretical instruction, but some firms have used actual HCF instructions to diagnose computers or simulate certain events in a computer system. The common definition of Halt and Catch Fire is that the instruction would cause the computer to lock up, and the user would need to restart it to be able to use it effectively.
Halt and Catch Fire instructions can be implemented in many different ways. One common type of HCF instruction would turn the address bus into a reader – in other words, the program would begin to loop by reading large amounts of data consecutively. This is one type of HCF method documented in the creation of an HCF instruction for a Motorola 6800 microprocessor in the 1970s. Experts pointed out that this type of sequential reading turns out indicators and report content that programmers and others can look at to evaluate the general performance of the CPU.
Halt and Catch Fire is also related to other types of situations that can lock up computers, such as the Pentium FOOF bug, which locks up the computer by referencing a nonexistent memory address.
In a way, Halt and Catch Fire is essentially a turn of phrase. It engages a common mythical or metaphoric conception around computers – namely, that overworking a computer system would cause it to overheat and literally burn or burst into flames. Especially with modern technology, this is entirely figurative – rather than burning, the system would just shut down.