As I recall MacOS system calls were done through invalid instructions which would cause the CPU to "trap" (raise an interrupt). Giving rise to the question Mac extension writers asked of each other: "How many traps did you patch?"
You want to talk trap patches? Your Mac's INITs have minimal trap patches, touch the Toolbox in boring places like SysBeep() and GetNextEvent(). The Developator's Mac has big, tricky INITs with trap patches that hook into half of the Device Manager.[1] The Developator is in touch with the metal, starts like a warm boot off the ROM reset vector, stops on an NMI.
The question serious patch trappers ask is whether you patched the traps used to patch traps to make sure that, when you patched traps, no other INIT could patch those traps after you to get in line before you when the traps were handled.
