256 Mb DRAM is organized as a 32M × 8 memory externally and as a 16K × 16K 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?

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256 Mb DRAM is organized as a 32M × 8 memory externally and as a 16K × 16K 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?

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UGC NET Computer Science (Paper 2) 17 June 2023 Official Paper

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6.6%
3.3%
9.9%
4.3%

Answer 1

The correct answer is 3.3%

SOLUTION:

To calculate the fraction of total memory bandwidth lost to refresh cycles, we need to consider the time spent on refreshing compared to the total time available.

First, let's find out how many rows are there in the DRAM:

Now, let's calculate the time required to refresh all rows:

Now, let's find the time available for data access in one refresh cycle:

Time Available for Data Access=499935600 nsTime Available for Data Access=499935600 ns

$\text{Time Available for Data Access} = 499935600 \text{ ns}$

Finally, let's find the fraction of time lost to refresh cycles:

Now, let's compare this result with the given options:

The closest option is 3.3%, so the correct answer is: 2) 3.3%

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