Project ForgeA main memory unit with a capacity of 4 megabytes is built using 1M×1-bit DRAM chips. Each DRAM chip has 1K rows of cells with 1K cells in each row. The time taken for a single refresh operation is 100 nanoseconds. What is the time required to perform one refresh operation on all the cells (expressed as a coefficient × 2^10, in nanoseconds)?
Explanation
A refresh operation refreshes one entire ROW at a time, across all chips simultaneously (since they share row-address lines). Each chip has 1K=2¹⁰ rows, so 2¹⁰ refresh operations suffice for the whole memory unit regardless of chip count. Total time = 100 × 2¹⁰ = 102400 nanoseconds.
Source: GATE CS 2010 (2010)
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