Delay line memory was used in the earliest digital computers. It was a type of refreshable memory that was serial access (sequential). Delay line memory works by having tubes of mercury that store and sending in pulses then having the other part of the memory decode the pulses. Dynamic Random Access Memory (DRAM) is used in most modern memory devices. It works by storing each bit of data in a separate capacitor in an integrated circuit. Like the delay line memory, it is a refreshable memory, but this is also a preventative measure because if power is not refreshed in a capacitor, they will leak charge and lose data. Neither memory can store data once power has been turned off.
