I have SAPPHIRE HD 7950 3GB GDDR5 WITH BOOST gpu. So sapphire owners, what does that pcb button do? How should I let it be? I don't see any difference at performance if I toggle it on/off.
http://www.sapphiretech.com/presentation/product/product_index.aspx?pid=1547&lid=1
It's small and would not be noticeable, but it's something.
That button is for your firmware/BIOS switching. Your card has a dual firmware/bios on it, so you can Flash one of them to be Overclocked, and have a backup in case you mess something up.
Some people say that one of them is not voltage locked, but the other is. But with my card, both were locked.
In short, if you dont flash your GPUs formware/bios, dont worry about it, it wont really matter.
Thanks for clarifying of that function.