Reprogrammable Microcode
Recent Intel processors (P6 and P7) have reprogrammable microcode. The BIOS may contain patches to the processor code to allow errors in the initial processor code to be fixed, updating the processor microcode each time the system is powered up. Otherwise, an expensive processor swap would be required. For example, the Pentium FDIV bug became an expensive fiasco for Intel that required a product recall because the original Pentium did not have patchable microcode.
Read more about this topic: BIOS, Changing Role of The BIOS