Grub MBR an enigma

[Thorny]

[...]
> 
> So are we saying here that 2 different OS on 2 different drives can both
> show the boot ID and be able to have a successful dual boot? Because
> when I receive error 21 (cannot boot)and there is a boot ID on 2
> different OS removing one allows me to dual boot
> 
> 
Allen, I would have to know the details of the exact situation to answer
further about what happened in your case.

But as an example, the system I'm typing this on currently has 3
physical hard drives with a total of 17 logical partitions, 2 of those
physical drives have one of their partitions marked with the boot flag
the other drive has only logical partitions. It is a multi-boot system and
it works.