There are four bank select bits to select up to 16 banks within each DRAM: two bank address bits (BA0, BA1), and two bank group bits (BG0, BG1).
每個DRAM裏有4個bank選取位元可用來選取多達16個bank單元：兩個bank位址位元（BA0、BA1），和兩個bank群組位元（BG0、BG1）。