What mobos need a fan on northbridge?

[theplanb]

I saw a nforce system with a heatsink on its..southbridge! :Q
And naturally HSF on its northbridge..
Now.. do we really need a fan on northbridge?
What chipsets require you to install a fan on a northbridge?
Intel, or AMD..

 

[rommel]

those that require them come with them already attached from the manufacturer...and yes if it has it on there it is needed

 

[RobsTV]

Why do the Abit boards that normally can do 143MHz FSB have a fan,
while the Iwill boards that can normally do 160MHz FSB have no fan?

I have even seen reviews that said adding a fan to the Iwill and
you could get another 10MHz. Is the Abit fan doing nothing??