My board has Dual BIOS, what does that mean? Do both BIOS function simultaneously?

On GIGABYTE motherboards with DualBIOS there are physically two BIOS
chips. For simplicity we'll call one your "Primary" BIOS and the other
we'll call your "Secondary" BIOS (your "hot spare").

If your "Primary" BIOS fails, the "Secondary" BIOS automatically
takes over on your next system boot. Automatically and with virtually
zero down time!

Whether the problem is a failure in flashing your BIOS or a virus or a
catastrophic failure of the primary BIOS chip, the result is the same -
the second BIOS backs you up, automatically!

Here's a link to Gigabyte Diagram of Dual BIOS operation:

http://www.gigabyte.com.tw/home/showbios.htm