Even the awkward segmentation on 8086 was arguably a form of memory protection. Minix on 8086 was surprisingly robust in practice (obviously not in theory) as

Even the awkward segmentation on 8086 was arguably a form of memory protection. Minix on 8086 was surprisingly robust in practice (obviously not in theory) as a rogue 'near' pointer would usually only corrupt the current program. But on the original topic, yes once you've got a 286+ there's no excuse for your OS not having true memory protection.