I've done a lot of partitioning / dual booting on my Macbook Pro. Right now I have Mac OS X installed along with Ubuntu 12.04, with Grub installed on the Ubuntu partition.
I am wondering - what is the code in my MBR (the first 446 bytes)? Because Macs use EFI and GUID partitioning, the MBR is only a protective/hybrid MBR (in my case, it is a hybrid MBR).
Q: How can I identify what program is in my MBR (based on its hexdump)? Is there some sort of a signature? I'm guessing it's grub but I did a hexdump of it and it didn't match the code I found in this article detailing the Grub MBR ("Stage 1") code.
EDIT: I am runnning rEFInd, an EFI bootmanager program. It is an EFI application, and thus resides on my EFI system partition. This program is what runs immediately following bootup, but I do not think it places any code in the 446 bytes of the MBR.
EDIT2: I should add that I have had Windows installed for dual-boot as well.