Dell dimension 3100 motherboard atx or micro atx?

hi ive been seaching for a while now. and it seems i cnat find wat i needed. im planning to upgrade my dell dimension 3100 mobo to xfx 750i extreme mobo which is atx. but i need to know first if the motherboard that came up with dell is atx or micro atx. the mobo number of dell is JC474. htanks!