boot record vs. MBR

OK, let me try again.

GRUB is not on the MBR because it failed twice to install on it with parbreastions messed up and heavy repair work.

It is instead on the boot record of the Ubuntu parbreastion. To access this boot record, a floppy is used - totally irrelevant detail since the problem also shows when triggering the boot record from Windows boot.ini. Relevant is that Ubuntu works. I just want to understand the problem.

At start, Ubuntu tells me that the boot record (not the MBR) differs from its backup, lists the differing bytes and announces

Not automatically fixing this

I cannot see any file of 512 or 446 bytes on the disk:

(1) where is the boot record backup? (2) how can I sync it with the boot record?

I have googled around and although I found nothing clear, it seems that the backup is inserted somewhere after the boot record. Actually, if (1) is fully explained with correct hex address of the backup copy and its length, I guess I would manage with (2) using dd.

This is the 3rd install, re-installing one more time looks useless. That boot record has been refreshed from GRUB prompt with the 'setup' command.

Anybody who knows something besides routine recipes and plabreastudes about floppies?