As I understand it, BIOS passes over to the hard disk marked as 1st priority, and reads the MBR from that disk.
BIOS wouldn't freeze. If it was unable to find a suitable disk to boot from it would come up with an error stating non-system disk, or OS not found, or words to that effect.
I boot my PC with 1x SSD, 1x 320GB WD, 1x 1TB F3, and 2x 2TB F4's, and just set my SSD as the first disk in the hard disk priority preferences.