5 ms·
Finally an OS that uses all four protection rings of x86 CPUs? :)
by johndoe0815 4y ago
Finally an OS that uses all four protection rings of x86 CPUs? :)
- fredoralive 4y agoIt 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.
- pjmlp 4y agoAlso one that doesn't follow the C church and was a pity that lost to the "freely available" UNIX derivatives, ending up supporting POSIX as well. Quite nice BASIC and Pascal compilers, and BLISS at least has facilities for proper bounds checking.