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It seems x86 rings don't quite work like a VAX’s, so they have to emulate them. The issues you have trying to run a Real OS on a Toy CPU… (ducks)
by fredoralive 4y ago
It seems x86 rings don't quite work like a VAX’s, so they have to emulate them. The issues you have trying to run a Real OS on a Toy CPU… (ducks)
- johndoe0815 4y agoInteresting, did the VMS team publish something about the emulation? That would be interesting for my OS course...
- fredoralive 4y agoThe 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.
- javitron 4y agoI don't think OpenVMS has run on VAX for a very long time.