Does Classic under OSX benefit (indirectly) from the Unix foundation it runs on: Is it, in other words, in any sense multithreaded, or does it run in a single unix "thread," is there protected memory, and does it have any advantge viz. preemptive multi-tasking etc.? Or is Classic simply what MacOS always was, effectively self-contained within some wider unix process?

System 7 under A/UX was single-threaded, did not offer protected memory, and offered only the standard, limited MacOS multitasking capability of plain-Jane System 7, so is MacOS9 running under OSX effectively the same?