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Code at 0x9F00 segment after boot (Miscellaneous)

posted by tkchia Homepage, 09.11.2020, 17:23

Hello Zyzzle,

> But, isn't it possible to boot through LILO and / or GRUB in Linux UEFI
> bootloader, and then load (emulate?) legacy MBR mode, and pass this code by
> in order to then boot native DOS? I hope it is so.
The main problem is that you need a legacy BIOS (or an emulation of such a thing) which knows how to talk to the classical MBR or floppy disk bootloader.

The classical bootloader needs to invoke legacy BIOS services --- as documented in Ralf Brown's Interrupt List and elsewhere --- to read disk sectors, write to the screen, read from the keyboard, find the amount of conventional memory, etc.

UEFI also has similar services, but the programming interface is totally different. So a bootloader will need to talk to UEFI in a totally different way. Alternatively, the boot disk must have some extra code to emulate enough of the legacy BIOS "on top of" UEFI, for stuff to work.

And that is the hard part. :-\

(I am kind of hoping that there is some sort of existing code project which tries to do this emulation. Because it seems this stuff is indeed hard.)

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

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