Before a read cycle we precharge both bit lines BL and BLB, i.e. drive the bit lines to a threshold voltage.Then we assert the word line WL, enabling both the access transistors which causes that the bit line BL voltage to either slightly drop or rise which is sensed by sense amplifier.
Hi,
Bank means a collection of registers or memory devices.As mentioned by Rahdirs the precharge circuit is used to charge the capacitors on the bit lines.Because the Capacitors play a major role in order to read and write.