> -----Original Message----- > From: Mark Knecht [mailto:[EMAIL PROTECTED] > Sent: 07 September 2005 20:12 > To: gentoo-user@lists.gentoo.org > Subject: Re: [gentoo-user] grub over the top of Win XP
[snip] > As for the comment above about BIOS order, I think that's correct, > but I tried an experiment on this machine and told it to boot from the > second EDIE controller. That did not change the order grub saw the > drives so I'm not sure every option in BIOS would fit your rule above, > or maybe I still don't understand. Without knowing the options of your BIOS I can guess two possibilities: a) your change was temporary and was not saved in the BIOS settings; b) your grub.map retained the old mapping of devices and that's what was followed. > The one thing that always confuses me is the difference between > placing grub in the MBR and placing it in a partition. It is my > understanding that the MBR is a separate part of the drive structure, > and is not part of any partition. Is this true? Yes. > When we place an bootloader in the MBR that's what the system jumps to > first? That's what the BIOS jumps to. The system is still inactive data scattered on the respective OS partition. > After that the bootloader in the MBR can transfer to either an > operating system or to a second boot loader. Not exactly: after that, the bootloader jumps to the boot sector of a partition (also called Partition Boot Record PBR). It is the code in the boot sector of a partition that will be loading the boot files which will bring up the OS (bootstrapping). The PBR also contains the Parameter Table outlining the layout and file system of the partition. Note here that the PBR refers to the boot partition (i.e. the partition that contains the boot files e.g. ntldr et al for WinXP or the Grub Stage2 files for Linux.) This can be different to the OS partition sector. > However, what Windows does is a bit beyond me. I suppose it places > it's own bootloader in the MBR. A *single* booting WinXP will follow the same process as I describe above (the multiboot M$Windoze arrangement is a bloody mess because it mixes up the boot files and partition boot sectors of the various M$Windoze operating systems on the drive). As you say, WinXP places its own boot loader in the MBR and it also configures its own PBR. Both of which are proprietary M$ code that Grub cannot read (hence the need for the 'noverify' to avoid Grub hanging). When we chainload WinXP using Grub or Lilo we jump to the WinXP PBR and pass on the controls to the PBR-->ntldr-->WinXP_kernel_image for it to boot. > We then overwrite it, but then we have > a command to jump to that OS. (chainloader +1 I suppose?) The chainloader +1 points Grub to load the first sector in the partition we specify. This is where the PBR exists which thereafter takes over to load WinXP. In the non-chainloading boot process (i.e. when Grub boots a system directly, like Linux) Grub will load the Stage2 boot files, which will load the kernel image. I hope this helps. -- Regards, Mick -- gentoo-user@gentoo.org mailing list
