DRAM standards and DDR4 timing

What is DRAM?
Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an IC. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory. And unlike non-volatile firmware chips, both DRAM and SRAM lose their content when the power is turned off.