A 4 MB main memory uses 1M×1-bit DRAM chips. Every chip has 1K rows of 1K cells. A refresh operation takes 100 ns. Find the time to refresh every cell once.
One refresh services a full row. Each chip has 2¹⁰ rows, so 2¹⁰ refresh cycles are needed. The memory’s thirty-two chips refresh in parallel rather than sequentially. Total is 100×2¹⁰ ns=102400 ns, B.
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