I believe that in the early alero years, all cars had disc brakes all around. Later ones added it as an option. Mine (04) has rear drums

. Anyways, to know what your car is just look at your vin code and check this link.
http://www.aleromod.com/forums/showt...light=vin+code
I'm assuming Alero level 1 is GS and Alero level 2 is GLS.