What is the differene when it says 790X, 790FX, 790GX on AM3 Mobo.

for gfx cards it usually relates to different chips, or die shrunk , more performance, stuff like that, you should be able to find out off their website

More info.

The important numbers:
First digit is the generation in the series (higher = newer)
Second digit is the level of performance (higher = enthusiast, lower = budget)
Third digit indicates updates, revisions, or new features (higher = new features since the previous one)

The important letters:
F = Fast or "F'ing awesome," basically a good overclocker
G = has onboard graphics
X = CrossFire capable

basically the FX can do 16x/16x crossfire
the GX has on board graphics and does 8x/8x crosfire
the X has no on board graphics and does 8x/8x crossfire
each chipset is as good as each other at ocing its judt the features and crossfire performace that is different

Thanks that clears up everything, dont need onboard dont need x16 x16 =P guess ill make sure i get X.

good luck w ur new build!