When referring to DDR/DDR2/DDR3/DDR4 memories, I am not able to understand the difference between memory clock and I/O clock.
DDR-200 - Memory Clock = 100 MHz, I/O Bus Clock = 100 MHz;
DDR2-800 - Memory Clock = 200 MHz, I/O Bus Clock = 400 MHz;
DDR3-1600 - Memory Clock = 200 MHz, I/O Bus Clock = 800 MHz;
DDR4-3200 - Memory Clock = 400 MHz, I/O Bus Clock = 1600 MHz
Could someone please explain what is memory clock and I/O bus clock here? Because I understand that memory controller provides only a single clock to the memory chip, which is half that of the data rate.