[CentOS] Re: Installation problem, possibly RAID

Bryan J. Smith b.j.smith at ieee.org
Sun Sep 11 11:04:31 UTC 2005

On Sun, 2005-09-11 at 06:40 -0400, Edward Diener wrote:
> In general Linux's reliance on partition order in mounting hard disk partitions, 
> and evidently grub's reliance on specific hardcoded hard disk geometry in order 
> to find its root partition, seem primitive to me. I could be wrong but I thought 
> that hard disk information on PCs was a pretty well determined thing and a 
> better system would automatically detemine these things at run-time. Of course 
> MS Windows does not allow a separate boot partition at all and also relies on 
> partition order, so my remarks go to Windows as well as Linux.

Windows can _only_ boot off of BIOS disk 80h (i.e., first).  That's the
limitation of not only the MS MBR, but both IO.SYS (DOS) and NTLDR (NT).
In the case NT loader, this is known as the "System" volume (and,
ironically, the partition that holds C:\WINNT is the "Boot" volume).

Linux can boot off of an array of different partitions, disks, etc...
In fact, Linux can load _multiple_ disk drivers in its initrd at boot.
NT can only load 1 additional vendor driver (ntbootdd.sys).
There are other advantages to Linux as well.

The trade-off -- on the PC BIOS architecture -- is that Linux _must_ map
the BIOS disk numbering to Linux devices.  That's why GRUB, LILO, etc...
have an issue when the BIOS disk numbering/order is changed -- because
it screws up assumptions.

The MS MBR blindly assumes BIOS disk 80h is correct.  Then it blindly
assumes what slices the bootstrap/NTLDR is at.  If it guesses wrong,
game over.  Although a NT5 (200x/XP) boot disk has "fixmbr" (MBR) and
"fixboot" (bootstrap/NTLDR) are on.

Try dual-booting Microsoft systems with their loaders -- let alone to
multiple disks without going into the BIOS and "hiding" some.

> In these days of large hard disks, boot loaders which can boot multiple 
> operating systems, and partition managers which can move and image hard disk 
> partitions at will, a better system for OSs to find what they need on hard disks 
> is needed.

It's a problem _only_ with (largely) the PC.  Don't get me started.  @-p

Bryan J. Smith     b.j.smith at ieee.org     http://thebs413.blogspot.com
The best things in life are NOT free - which is why life is easiest if
you save all the bills until you can share them with the perfect woman

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