Suppose a DRAM memory has 4 K rows in its array of bit cells, its refreshing period is 64 ms and 4 clock cycles are needed to access each row. What is the time needed to refresh the memory if clock...

Suppose a DRAM memory has 4 K rows in its array of bit cells, its refreshing period is 64 ms and 4 clock cycles are needed to access each row. What is the time needed to refresh the memory if clock rate is 133 MHz? What fraction of the memory's time is spent performing refreshes?