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0 pointsVogonPoetry4mo ago0 comments

I agree that my comment about VM was imprecise and inaccurate.

I do dispute your assertion that virtual memory was "disabled". It isn't possible to use V86 mode (what the Intel Docs called it) without having a TSS, GDT, LDT and IDT set up. Being in protected mode is required. Mappings of virtual to real memory have to be present. Switching in and out of V86 mode happens from protected mode. Something has to manage the mappings or have set it up.

Intel's use of "virtual" for V86 mode was cursory - it could fail to work for actual 8086 code. This impacted Digital Research. And I admit my experiences are mostly from that side of the OS isle.

I did go back and re-read some of [0] to refresh some of my memory bitrot.

[0] https://www.ardent-tool.com/CPU/docs/Intel/386/manuals/23098...

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trollbridge4mo ago

Slight nitpick: you could run fire up V86 mode without any LDT entries.

It's also possible to run Virtual 8086 mode without paging enabled, and when in Virtual 8086 mode, the 386 doesn't care about what's in the LDT/GDT (unless an interrupt happens). In practice this is never done because the Virtual 8086 task would only be able to use the bottom 1MB of physical memory.

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