256 Mb DRAM is organized as a 16 K × 16 K memory externally and as a square array internally. Each row must be refreshed at least once every 50 mili second to forestall loss of data; refreshing one row takes 100 nanoseconds. What fraction of the total memory bandwidth is lost to refresh cycles?

1. A6.6%
2. B3.3%
3. C9.9%
4. D4.3%

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Correct answer: B. 3.3%

Explanation

16K rows × 100 ns = 1.6384 ms of refresh in every 50 ms. Fraction = 1.6384 / 50 ≈ 3.3%.