4 protection rings of x86 are mostly not usable for anything, as they apply to descriptors, not memory page (there is only single user/supervisor bit in page ta

4 protection rings of x86 are mostly not usable for anything, as they apply to descriptors, not memory page (there is only single user/supervisor bit in page table entry). The whole 286 descriptor based memory protection model is mostly unusable for C-and-separate-processes multitasking model (and has relatively significant overhead).