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What is this 32-bit real mode mentioned in the official Intel x86 x64 manual?

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ben321:
I was just reading the second page of section 8.1.10 (go to https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-1-manual.pdf#G9.57567 and then go down one page) in the official Intel CPU manual, while researching on the x87 FPU I happened to notice something interesting. It mentions a 32-bit real mode. And I'm thinking WOW, how does that work? I've always been told that real mode is 16 bits, and that there are 16bit and 32bit protected modes (and now also 64bit long mode). Is this an experimental mode that Intel was working on, but just never developed a CPU for? Or is this some kind of mode that while it does exist in Intel CPUs, the mechanism to switch to it is undocumented?

And by the way, that one mention of 32bit real mode, is the ONLY mention in the entire PDF file. And the file contains almost 500 pages.

Frank Kotler:
Possible reference to djgpp?

   www.delorie.com/djgpp/

Best,
Frank

debs3759:
https://en.wikipedia.org/wiki/Unreal_mode

debs3759:

--- Quote from: Frank Kotler on October 09, 2022, 12:32:11 AM ---Possible reference to djgpp?

   www.delorie.com/djgpp/

Best,
Frank

--- End quote ---

Unreal mode is fairly well documented. Best reference I can find with code examples is https://wiki.osdev.org/Unreal_Mode

Frank Kotler:
Yes. Sometimes referred to as "voodoo mode" or "flat real mode". Better called "relimited real mode", perhaps. Fasm used it at one time, I think. Not much used these days I suspect., unless you're in a museum... in the basement...

Best,
Frank

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