when vendors write new code for the mb bios they rename the file to a new rev. http://www.asus.com/Motherboards/Intel_Socket_1155/P8Z77V/#download
the first code was the x800 code. then as they did bug fixes for the mb they make a new bios file and renumber it.
on the box or the mb may be a mb bios rev sticker. if you cant find it try flashing the bios with 900 bios to see if it fixes your issues.