What does two input and one output buffer like gate do?
This is a tri-state buffer. When the control signal (Read/NotWrite) is high, the data signal is propagated from "Data In" to whatever is connected to the right. When it is low, there is a virtual disconnect between "Data In" and the output of the buffer. In case of DRAM it might be used to select a function of the data pin to be either input or output.