It will restore the Operating system to the state it was originally in when it left the factory. It will not affect the BIOS.
So in supportassist os recovery, there is an option for resetting the laptop to factory settings, it says it will restore everything to when it first left the factory.  My question is, does this restore the bios version to the original one too?  The first BIOS Installed when I got my Alienware m15 r1 was 2.5, now it's 2.9, so will it restore it to 2.5 if I choose that option? 
Does 'reset to factory settings' in supportassist OS recovery restore original 
BIOS?