DRAM

A bit is formed by a capacitor and a MOSFET gate. The capacitor restore the bit. 

To read, the control line of the gate is raised to drain the capacitor which represent a one of charge was stored. The current rent is latched in the chip output register for cpu.  To write, the control line is raised again to allow current flow to the capacitor but this time is to charge it. 

Capacitor leaks over time. So there is a need to recharge it and current recharge cycle is about 64 ms. The bit is read off and store back again in the refresh cycle.