GRUB discussion follow up ?

[William Case]

Hi Jacques;

On Sun, 2007-10-21 at 16:29 -0400, Jacques B. wrote:
> On 10/21/07, Robert P. J. Day <rpjday at crashcourse.ca> wrote:
> > On Sun, 21 Oct 2007, Jacques B. wrote:
> >
[snip]
> 
> I'll have to check out beyond the 1K mark, as well as check out
> grub-install.  Also I noticed my touch typing was off a bit.  I put 15
> bytes instead of 16 bytes X 4 for the partition table.
> 
> Seeing grub has to do with booting, as a slight tangent any suggested
> readings for the Linux boot process (actually not only Linux, but
> including Grub & Lilo boot loaders).  I found some (it's back at the
> office) when I was digging into the boot process a while back.  I was
> also looking at the possibility of using bootchart from bootchart.org
> as a tool to better understand the boot process.  Anybody play with
> that?  If so your thoughts on using it to better understand the boot
> process...  Sorry if I'm hijacking this thread.  Hopefully it falls
> within the realm of grub discussion follow up.
> 

I don't see it as hijacking.  It certainly follows up on the Grub
discussion.

I have been scratching around as well.  I came up with more new
questions than answers.  But it seems to me that understand GRUB, it has
to be completely disambiguated (to borrow a Wikipedia term) from Linux
or any other Operating System first.  Only then adding in how Linux gets
loaded.

That means understanding the following in their proper order:
1) BIOS in general
2) How BIOS originally writes disk and partition locations to the MBR
or after installing a new harddisk. It must have some BIOS info even if
'fdisk', 'parted' or 'mkfs' are used as part of the installation.  I
don't know if these are even involved but I plan to check.
3) What code system it uses to designate disks and partitions.  I have
found three or four sites that break down the meaning of binary code bit
by bit.  That needs study.
4)How to install Grub on a cd-rw.  That will separate the men from the
boys and explain how BIOS finds GRUB and how GRUB finds the operating
system.  It should also explain how stage 1.5 gets where it is going.
5) How the MBR binary code might vary from the code GRUB uses?
6) Does GRUB get its disk and partition information from BIOS ROM/CMOS
or from RAM after BIOS has been loaded?
7) Where is stage 2 installed?  How big is it?  It seems to have a lot
of different file systems data and CLI commands available for just a
tiny system.  How does it use the grub.conf file?  Is it just a C
compilation or does it have some aspects of an interpreter?
8) (more properly 5b)) Because GRUB is so rudimentary and used so early
in the boot process, what processes and data are NOT available to it
until an operating system is loaded. Or, does it have a way of getting
at some data before Linux is loaded eg device.maps, system.map and
menu.lst/grub.conf.  How does it use /boot/grub/e2fs_stage1_5,
fat_stage1_5, reiserfs_stage1_5 etc.?
9) Where does the menu gui come from?
10) When -- exactly -- (on what line of GRUB code) does GRUB begin
loading the Operating System?
11) How does it load from a cd-rom, from a stand alone partition, from
another computer?  Particularly if no other system is yet running.
12) One more disambiguation between GRUB and the Operating System

Jacques, your points have given me an opportunity to list the current
questions I have.  I know I have found some of the answers already.  I
just have to read through them and put them all into a meaningful
context.  Other questions and answers I now feel confident I can chase
down. (Probably have to look at some source code.  I hope not -- that
can become a cascading disease.)

-- 
Regards Bill