Hi Paul,

> That's because on a AHCI only computer (without PATA or SATA IDE),
>  you cannot access the sectors with INT 13h.

Yes you can. For harddisk/SSD. Unless you configure the
computer to disable BIOS completely and boot only UEFI
operating systems.

But in that case, you get plenty of other problems and
should really load a CSM to get BIOS services for DOS.

If switching the simulated controller to AHCI breaks
BIOS services in QEMU, that simply is a bug in QEMU.

For the hypothetical situation that you want to boot
from a drive without BIOS support, you can do as EZ
DRIVE and similar drivers did in the 1990s: Load your
driver BEFORE DOS and let it provide the BIOS int 13
services. Your driver will probably have to be some
form of UEFI boot loader in that case, which means
it would be better to load a CSM in the first place.

However, if you boot from CD / DVD, you actually get
the opposite effect: El Torito support is activated
and makes it easy to have BIOS style CD / DVD access.

Also, you can use MEMDISK to init bootable ramdisk
contents from any type of drive which is supported
by GRUB, ISOLINUX and other Linux boot tools :-)

Regards, Eric



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