Halt and Catch Fire
6 hours ago
- #hardware bugs
- #programming humor
- #computing history
- Halt and Catch Fire (HCF) originally referred to machine-code that halts the CPU and requires a reset to recover, with the phrase stemming from engineering humor and IBM System/360 stories where overheating could cause fires.
- The Motorola 6800 had undocumented opcodes, like $9D and $DD, that led to HCF behavior—causing the program counter to rapidly cycle through memory without executing instructions, only stoppable via reset, as detailed in Gerry Wheeler's 1977 BYTE article.
- HCF evolved into a broader term for processor-locking opcodes, including the Pentium F00F bug and other hardware vulnerabilities, highlighting how fuzzing techniques today uncover similar issues in modern processors.
- Interestingly, some engineers repurposed HCF-like behavior for practical uses, such as RAM scanning, turning it into a 'happy accident' in hardware testing.