Which of the following description about memory hierarchy in multiprocessor syst

Question

Which of the following description about memory hierarchy in multiprocessor system is NOT correct.
Choose one answer.
a. Cache consistency determines when a written value should be returned by a read
b. Cache coherence only guarantees that all processors see the same value for the same memory address at the same time
c. For a cluster with thousands of processors, the snooping protocol can help to maintain coherency.
d. A processor can cause cache misses for another processor even though they are working on unrelated variables

Explanation / Answer

Memory hierarchy in multiprocessor systems:

Correct Answer is (B):

Cache coherence only guarantees that all processors see the same value for the same memory address at the same time.

Explanation:

Above statement is incorrect. Because cache coherence does not return the same value, for every time, memory address are changes from operation to operation and time to time.

Consider the option (A):

Cache consistency determines when a written value should be returned by a read.

Explanation:

The above statement is correct. Because cache memory is reads the data, which frequently writes from the main memory after read.

Consider the option (c):

For a cluster with thousands of processors, the snooping protocol can help to maintain coherency.

Explanation:

The above statement is correct. Because snooping protocol idea is to maintain transactions on monitor are visible to all processors.so it can take an action to ensure coherence.

Consider the option (d):

A processor can cause cache misses for another processor even though they are working on unrelated variables.

Explanation:

Depend on the block size it can cause read and write misses. Large blocks can cause false sharing where two unrelated shared variables are located in the same cache block, the full block is exchanged between processors even though the processor are accessing different variables

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