This is something of a FAQ but we don't have a FAQ list :-)
Cathy A explains it here:
http://giftedissues.davidsongifted.org/BB/ubbthreads.php/topics/64708/FSIQ_and_GAI.html
and here's another relevant thread:
http://giftedissues.davidsongifted.org/BB/ubbthreads.php/topics/71384/FSIQ_vs_GAI.html
There are others - I just googled
GAI FSIQ site:davidsongifted.org
which works rather better than using this site's search function, I find.

Hope that helps!

Email: my username, followed by 2, at google's mail