GoKawiilI have never watched the AMC show Halt and Catch Fire, and for a long time I only knew the title, but nothing about the show. Something about it always reminded me of programmer humor: somewhat dramatic, a little absurd, and weirdly precise. Turns out, the show really is about the computer industry in the 1980s and 1990s, but the phrase itself is much older than the show, and it started as some engineering humor.
What it means
In the context of computers, Halt and Catch Fire (shortened to HCF) has been generalized to describe machine-code that causes the CPU to stop doing anything useful, forcing you to only recover by resetting (or power-cycling) the machine. In a pretty literal sense, it "halts" the machine. Sure, the "catch fire" part is a joke, but it's not as far-fetched as it might seem. Take the IBM System/360 for example. Apparently when this system would encounter a certain invalid opcode, it would constantly access a specific location in the magnetic core memory, which caused it to get very hot and even catch on fire.
Over time, HCF also became a catch-all label for undocumented or invalid opcodes that lock up the processor, intentional test modes that look like a hang, and real hardware bugs (you might even recall that some early Pentium-class chips could be locked up with a carefully chosen illegal instruction, known as the F00F bug - more on that later).
The phrase was created, in part, because of the standard of using three-letter assembly mnemonics: ADD , CMP , JMP , etc. The joke spread in various publications, including HCF alongside some other personal favorites of mine:
EPI : Execute Programmer Immediately
: Execute Programmer Immediately DC : Divide and Conquer
: Divide and Conquer CRN : Convert to Roman Numerals
The Motorola 6800
So HCF was mostly just a joke, until it wasn't.
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