<P> On the Zilog Z80, executing DI (disable interrupts) followed by HALT (wait for an interrupt) results in the CPU staying frozen indefinitely, waiting for an interrupt that cannot happen . The similar processor found in the Game Boy contained a partial fix allowing it to recover from one HALT, but it would become frozen with two consecutive HALTs with interrupts disabled . </P> <P> It should also be noted that the Z80 supports a non-maskable interrupt . The / NMI signal is on Pin 17 of the original 40 pin DIP package . Since a non-maskable interrupt will regain control of the CPU even after executing the instruction sequence DI / HALT, that pair does not represent a true HCF, it will only result in a HCF condition if either the / NMI pin is connected directly to the + 5V rail, making the generation of that signal impossible, or if the interrupt routine that services / NMI ends with a return, placing it back in the HALT state . </P> <P> One apocryphal story about the HCF instruction in an actual early CPU goes back to the late 1960s, when computers used magnetic core memory . The story goes that in order to speed up the core memory on their next model the engineers increased the read / write currents in the very fine wires that were threaded through the cores . This worked fine when the computer was executing normal programs, since memory accesses were spread throughout memory . However, the HALT instruction was implemented as a "Jump to self". This meant that the same core memory location was repeatedly accessed, and the very fine wires became so hot that they started to smoke--hence the instruction was labeled "Halt and Catch Fire". </P>

Where did the phrase halt and catch fire come from
find me the text answering this question