[UFO Chicago] Bootloaders Able To Access The Entire Disk

Jay F. Shachter jay at m5.chicago.il.us
Wed Jun 3 11:41:57 PDT 2015

Esteemed Colleagues And Fellow Nerds:

Recently I acquired a laptop with an old BIOS, although I did not
suspect just how old, until it was too late.  This laptop's BIOS is
so old ("how old is it?") that it can only access the beginning of the
internal disk.  Historically this was the main reason for the custom,
on Linux, of placing /boot in a separate slice of disk toward the
start of the disk, while the bulk of the filesystem went elsewhere
(another reason was wanting to put the root filesystem on a logical
volume, back in the days when GRUB could not boot from LVM) -- because
on such computers, not only the BIOS, but also GRUB, cannot access the
entire disk.  Thus, placing GRUB at the beginning of the disk is
insufficient; the operating system that GRUB loads into memory must
also entirely reside toward the beginning of the disk.

I did not suspect that my computer was that old, until after I had
already partitioned its disk, and already installed FreeBSD
11.0-CURRENT, and LinuxMint 17.1, and OpenSUSE 13.2, and Haiku
alphaR4.  Haiku resides toward the end of the disk, in what, on Linux,
would be called sda7, and GRUB cannot boot it (this is Grub2, of
course).  GRUB does not even know that sda7 and sda8 -- or, as GRUB
would say, (hd0,7) and (hd0,8) -- even exist, it only knows about
slices up to sda6; if you try to say

   chainloader (hd0,7)+1

it complains about a "nonexistent partition", or words to that

Is there another bootloader able to load programs from a region of the
disk that the BIOS cannot see?  Or is there a module that GRUB could
insmod that would render it able to do so?  I do not see any reason
why this should not be the case.  The operating system that GRUB
loads, after GRUB brings it into memory, is able to see the entire
disk, including the parts that the BIOS cannot see; why should not
another bootloader, or indeed GRUB itself, be able to do the same?  I
do not require that GRUB know the filesystem on which the booted OS
resides (although, as it happens, GRUB2 does have a bfs module); I
only want to be able to boot operating systems like Haiku and IcarOS
that are equipped with their own minimal bootloaders at the beginning
of their disk slice, hence I need nothing more than "chainloader +1"
capabilities.  As always, thank you in advance for any and all

                        Jay F. Shachter
                        6424 N Whipple St
                        Chicago IL  60645-4111
                                (1-773)7613784   landline
                                (1-410)9964737   GoogleVoice
                                jay at m5.chicago.il.us

                        "Quidquid latine dictum sit, altum videtur"

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