[tinglymintyfrsh]

I'm trying to remember from the last em64t/ia32e & ia32 ISA toy OS I messed around with.

i386 ISA is the bare minimum for functioning protected mode to be better than real-mode DOS. i286 protected mode is absolute trash.

i386 is so bad at dealing with SMP primitives, it was standard practice to have a non-SMP kernel. Then, you get into the business of maintaining 2 kernel flavors or a major kernel feature flag.

For those interested, there is a quirky processor mode trick called "unreal mode" that allows flat addressing without switching to protected mode (no protections, just like real-mode DOS).