While trying to answer this question on askubuntu: How do I Uninstall GRUB I read the Wikipedia article on MBR and also the perfect answer on a somewhat related question here on Superuser, however, one thing is still not clear to me:
What exactly makes BIOS decide if a drive is bootable or not? How does the boot sequence skip from drive #1 and proceed trying to boot from drive #2 if more than one drive is installed in the system?
My understanding is that the only thing BIOS normally checks on an MBR is its signature at the very end of the 512-byte sector, and then it just transfers control to the initial bootloader situated in the first 446 bytes of the boot sector.
Does it imply that the first 446 bytes of the boot sector MUST contain some meaningful bootloader code even if the disk is not bootable?
After BIOS transferred control to the bootloader on drive #1 which happened to have no "bootable" partitions - how exactly is the bootloader on the second drive invoked?
Sorry if this is too technical :) Short question is: "How exactly does BIOS skip a drive and proceed to try to boot from the next one?"