Consider three memory-management systems S1, S2 and S3 that use simple paging fo
ID: 3793599 • Letter: C
Question
Consider three memory-management systems S1, S2 and S3 that use simple paging for memory management and employ associative registers to speed up page lookups.
Let S1 have a set of associative registers, with lookup performance of 120ns and a hit rate of 60%. Let S2 have a larger set of slower associative registers with lookup performance of 180ns and a hit rate of 80%. Let S3 have a set of associative registers with lookup performance of 120ns and a hit rate of 80%. Let the main-memory page-table lookup take 600ns in all the three systems.
In terms of the lookup algorithm, let S3 employ the serial algorithm where the lookup is first conducted in the associative registers and only after the lookup miss in the associative registers, the main-memory lookup is initiatied. In contrast, let S1 and S2 employ the parallel algorithm where the lookup is conducted in parallel in both the associative registers and the main-memory page table.
Determine the page-lookup performance for the three schemes. In particular, compute the average time for page lookup as well as the lookup time in the case of a page hit and a page miss. Based on this computation, identify the FALSE statement among the following.
Consider three memory-management systems S1, S2 and S3 that use simple paging for memory management and employ associative registers to speed up page lookups.
Let S1 have a set of associative registers, with lookup performance of 120ns and a hit rate of 60%. Let S2 have a larger set of slower associative registers with lookup performance of 180ns and a hit rate of 80%. Let S3 have a set of associative registers with lookup performance of 120ns and a hit rate of 80%. Let the main-memory page-table lookup take 600ns in all the three systems.
In terms of the lookup algorithm, let S3 employ the serial algorithm where the lookup is first conducted in the associative registers and only after the lookup miss in the associative registers, the main-memory lookup is initiatied. In contrast, let S1 and S2 employ the parallel algorithm where the lookup is conducted in parallel in both the associative registers and the main-memory page table.
Determine the page-lookup performance for the three schemes. In particular, compute the average time for page lookup as well as the lookup time in the case of a page hit and a page miss. Based on this computation, identify the FALSE statement among the following.
Explanation / Answer
In the case of S1, it takes 120ns for a page lookup and its hit rate is 60 % and 600ns if there is a page miss.
Thus, the overall page-lookup performance of S1 is 0.6 * 120 + 0.4 * 600 = 312ns
In the case of S2, it takes 180ns for a page lookup with hit rate of 80 % and 600ns if there is a page miss.
Thus, the overall page-lookup performance of S2 is 0.8 * 180 + 0.2 * 600 = 264ns.
In the case of S3, it takes 120ns for a page lookup with hit rate of 80 % and 720ns if there is a page miss
algorithm). Thus, the overall page-lookup performance of S3 is 0.8 * 120 + 0.2 * 720 = 240ns.
Therefore, S3 has the best overall performance while S1 has the worst overall performance.
Answer is D) D is FALSE here,
Truth is S3 has better performance than S2 as we can see 240 < 264
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