Halt and Catch Fire - in Early CPUs

In Early CPUs

The HCF instruction was originally a fictitious instruction, claimed to be under development at IBM for use in their System/360 computers, along with many other amusing instructions such as, "Electrocute Computer Operator".

One apocryphal story about the HCF instruction 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".