Consult your motherboard’s manual first as it details the correct place! In most cases if you only have 2 RAM sticks (a.k.a. DIMMS) and there are 4 slots on the motherboard, you should use the 2nd & 4th slots (A2 and B2). If you have 4 slots and 4 DIMMs, put the other two modules in the 1st and 3rd slots (A1 and B1).