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On a 286 you do not have access to real mode when in protected mode. You need a 386 for that. A crazy trick that did work is to cause a triple fault in protect

by phicoh 8y ago

On a 286 you do not have access to real mode when in protected mode. You need a 386 for that. A crazy trick that did work is to cause a triple fault in protected mode. That would reset the 286. Then there was a little bit of support from the BIOS. You could tell the BIOS to not run the power on self tests and load the MBR from disk. Instead the BIOS would jump to a specific memory location.

wolfgke 8y ago
> On a 286 you do not have access to real mode when in protected mode. You need a 386 for that. I think that you are mistaken: I am rather sure that the undocumented LOADALL instruction could make something like that possible: > https://en.wikipedia.org/wiki/LOADALL https://en.wikipedia.org/wiki/LOADALL
- wolfgke 8y ago
  Update: Indeed it is possible to use LOADALL to switch from protected mode to real mode: > http://www.os2museum.com/wp/loadall-strikes-again/ http://www.os2museum.com/wp/loadall-strikes-again/ Article found via https://retrocomputing.stackexchange.com/a/220/4889 https://retrocomputing.stackexchange.com/a/220/4889
  - yuhong 8y ago
    No it is not, the article was later corrected.
    - yuhong 8y ago
      Correct link BTW: http://www.os2museum.com/wp/will-the-real-real-mode-please-stand-up/ http://www.os2museum.com/wp/will-the-real-real-mode-please-s...