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Re: Triple boot:XP,ubuntu&FC5 grub failed



Jim Cornette wrote:

Lokking through the replies, I did not see mention of what installs the basics for the bootloader.

When you run grub-install /dev/hdx# from any of your installations, information is installed for grub to finis booting. So when you install grub into /dev/hdb2 for example, information for grub and the first stage is chainloaded. (given over control to the particular OSes version of grub.) From there, it loads the consecutive stages in a similar way that installing grub into the MBR does. If grub is not installed into

You were OK up to here.

the MBR, the partition where you installed grub into must be marked as active. BIOS will take it from there to start grub from a partition where it is installed, consecutively going through the various stages grub goes through in order to load the OS.

The BIOS does NOT search the partition table for an active partition.
It is the code in the MBR which does that. All the BIOS looks for
is the first physical sector on the physical volume having the BOOT
RECORD signature (AA55) in the last two bytes. The BIOS accesses the
disc in a physical manner (LBA translation aside). It knows nothing
about partitions. Indeed, there are more than one way of partitioning
discs, and the "traditional" method is not the only one. Anyway, if
the BIOS finds the BR signature in the first physical sector, then it
simply loads it to 0000:7C00 (IIRC) and jumps to it. [NB: The processors
all reset to REAL mode, so this is not a selector address, but a
segmented address.]

Mike
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