Originally eltorito.sys was only designed to work for a boot sequence like:
BIOS -> CD-ROM with no-emulation bootloader (for example syslinux) ->
memdisk -> DOS -> eltorito.sys
eltorito.sys continues to use the BIOS to access the device.

I discovered that eltorito.sys can be also used for CD-ROM devices which
haven't booted by BIOS or BIOS extender (for example bootable cd loader
is a BIOS extender).

One example is at http://grub4dos.sourceforge.net/wiki/index.php/DOS

You can also make the boot sequence like:
BIOS -> bootable harddisk (no matter if IDE, SATA or USB as long as
supported by BIOS or by BIOS extender) -> grub4dos -> DOS
even in this case eltorito.sys can access a CD-ROM.

The relevant example (tested and working) demonstrates this:
title booting FreeDOS from raw image (as harddisk) + FreeDOS installer
CD\nit's up to the operating system to load a device driver for the
virtual CD-ROM, for example:\ndevload eltorito.sys
/D:eltorito\nshsucdx.com /D:eltorito
map --unsafe-boot /FreeDOS.img (hd0)
map /fdfullcd.iso (hd32)
map --hook
chainloader --force (hd0)+1

Another example (not well tested) for a real CD-ROM, you use grub4dos as
a BIOS extender (works also if BIOS can not even boot from CD-ROM,
doesn't always work).
title boot hdd and initalize cd-rom
chainloader /kernel.sys
cd-rom --init
map --hook
here also devload eltorito.sys /D:eltorito ; shsucdx.com /D:eltorito
should make the real CD-ROM available to DOS using eltorito.sys.


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