[lug] boot loader mystery

[karl horlen]

> The bios understands where IDE disks are because it
> is coded into the
> bios.  The mbr is always in the same place on a
> disk, so the bios doesn't
> have to know anything about the file system on the
> disk or the operating
> system on it.  It just starts reading the mbr and
> wants machine code that
> the processor can understand.  In the case of SCSI
> disks, you'll generally
> see that they have their own bios which loads before
> the mbr is loaded so
> that you can boot off scsi disks.  I believe the
> bios needs the ability to
> talk to a scsi adapter in order for this to work.  I
> suspect it is a stub
> that just calls some agreed upon code to load
> awareness of devices.

That explains the first part of my question.  Each
adapter, whether onboard or installed as an expansion
card inserts it's own bios code for booting off that
controller.  One down one to go.
 
> the filesystem.  I think grub just stores where it
> thinks things are on
> disk to load them (this could use some
> clarification).  The bootloader
> loads the kernel.  

So that's the second part that still needs
clarification.  The bootloader (grub or lilo) itself
needs to know where on the disk the kernel(s) and or
initrd live.  That would seem to be location specific
as well and require a bios installed call to access
that since the driver isn't loaded yet.

So disk locations would seem to be necessary.
I think that might be what that map file is for in
lilo?  And that's probably why you need to rerun lilo
every time you make a change to it.  But I'm wondering
how grub knows the physical location of /boot?

thanks for the input


 
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