A dynamic RAM is refresh cycle of 32 times per msec. Each refresh operation requires 100 nsec and a memory cycle requires 250 nsec. What percentage of…
A dynamic RAM is refresh cycle of 32 times per msec. Each refresh operation requires 100 nsec and a memory cycle requires 250 nsec. What percentage of memory's total operating time is required for refreshes?
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Correct answer: (D) 0.32
Explanation
In 1 msec (10⁶ nsec) there are 32 refresh cycles, each taking 100 nsec, so refresh time per msec = 32 × 100 = 3200 nsec. Equivalently, per memory cycle of 250 nsec, refresh cycles = (32 × 250)/10⁶ and refresh time = ((32 × 250)/10⁶) × 100 = 0.8 nsec; percentage = (0.8/250) × 100 = 0.32%.