The source of the bit about VMS only using 2 rings on x86 from the Wikipedia article is https://www.youtube.com/watch?v=U8kcfvJ1Iec https://www.youtube.com/watc

The source of the bit about VMS only using 2 rings on x86 from the Wikipedia article is https://www.youtube.com/watch?v=U8kcfvJ1Iec https://www.youtube.com/watch?v=U8kcfvJ1Iec , which I did skim to check that source for what the differences were (it seems to be around page protection between rings[1], circa 14 minutes in). I assume it gives more information, but I don't have time to watch more of it. [1] Before I checked I was under the misunderstanding that AMD64 had just got rid of the extra rings alongside stuff like BCD instructions, so was trying to find a source for that.