[dansalvato]

This was popular on Amiga as well, although maybe less clean and "officially supported" compared to Mac OS system extensions. There were Amiga utilities that remapped OS system calls to custom functions with performance optimizations, enhanced functionality, or different behavior altogether.

The 68000 series CPUs didn't have an MMU built-in until the 68030, which I guess was far too late to see much use in consumer OSes. Pretty shocking that the jump to PPC wasn't enough for Apple to take care of that stuff, but I guess that was going to be Copland before it was canned. At least Amiga had preemptive multitasking from the beginning.