Made Easy Test Series 2024

Question

A dynamic RAM has a refresh cycle of 32 times per msec. Each refresh operation requires $100$ nanosecond and a memory cycle requires $200$ nanosecond. What percentage of memory's total operating time is required for refreshes?

Answer 1

0.32%

Comments

Here in one memory cycle, both memory access and refresh operation(not simultaneously) are performed ?

And when memory cycle time is given..then the refresh period is equal to one memory cycle time ?

Answer 2

Given, memory cycle time=200 ns= 200 x $10^{-9}$ s, Time taken for 1 refresh cycle=100 ns= 100 x $10^{-9}$ s, no. of refresh cycles=32 per msec= 32000 per sec

No. of refresh cycles in 200 ns= 32000 x 200 x $10^{-9}$ = 6.4 x $10^{-3}$
Time taken for 6.4 x $10^{-3}$ refresh cycles= 6.4 x $10^{-3}$ x 100 x $10^{-9}$ = 0.64 x $10^{-9}$ s
Therefore, Percentage of time for refresh = $\frac{0.64*10^{-9}}{200*10^{-9}}$ x 100 = 0.0032 x 100 = 0.32 %