Four transistors (T1, T2, T3, T4) are cross connected in an arrangement that produces a stable logic state.
In logic state 1, point A1 is high and point A2 is low; in this state T1 and T4 are off, and T2 and T3 are on .
In logic state 0, point A1 is low and point A2 is high; in this state T1 and T4 are on, and T2 and T3 are off .
Both states are stable as long as the dc supply voltage is applied.
The address line is used to open or close a switch which is nothing but another transistor. The address line controls two transistors(T5 and T6).
When a signal is applied to this line, the two transistors are switched on, allowing a read or write operation.
For a write operation, the desired bit value is applied to line B, and its complement is applied to line 
. This forces the four transistors(T1, T2, T3, T4) into the proper state.
For a read operation, the bit value is read from the line B. When a signal is applied to the address line, the signal of point A1 is available in the bit line B.