Cache Coherency MCQs

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1. : What is the primary goal of cache coherency protocols?
(A) To ensure all caches in a multiprocessor system have a consistent view of memory
(B) To increase the speed of cache memory
(C) To reduce the size of cache lines
(D) To manage cache replacement policies

2. : Which protocol is commonly used to maintain cache coherency in multiprocessor systems?
(A) MESI (Modified, Exclusive, Shared, Invalid) protocol
(B) LRU (Least Recently Used) protocol
(C) FIFO (First In, First Out) protocol
(D) Direct-mapped cache protocol

3. : In the MESI protocol, what state indicates that a cache line is both dirty and exclusively held by one cache?
(A) Modified
(B) Exclusive
(C) Shared
(D) Invalid

4. : Which state in the MESI protocol signifies that a cache line is stored in other caches and is not modified?
(A) Shared
(B) Modified
(C) Exclusive
(D) Invalid

5. : What happens when a cache line is in the “Invalid” state in the MESI protocol?
(A) The cache line is not valid and cannot be read or written
(B) The cache line contains stale data
(C) The cache line is exclusively held by one cache
(D) The cache line is dirty and must be updated

6. : In the MESI protocol, what must happen when a cache line in the “Modified” state is evicted?
(A) The cache line must be written back to main memory
(B) The cache line is discarded without writing back
(C) The cache line is moved to the “Shared” state
(D) The cache line is moved to the “Exclusive” state

7. : Which protocol uses the “Invalidate” command to maintain cache coherency?
(A) MESI
(B) MOESI
(C) MSI
(D) LRU

8. : What is the key difference between the MESI and MOESI protocols?
(A) MOESI includes an additional “Owner” state
(B) MESI includes a “Modified” state
(C) MOESI does not use an “Invalid” state
(D) MESI uses a “Shared” state, while MOESI does not

9. : In the MOESI protocol, what state indicates that a cache line is dirty and can be written back to memory?
(A) Owner
(B) Modified
(C) Exclusive
(D) Shared

10. : What type of cache coherence problem occurs when multiple caches hold copies of a modified cache line?
(A) Coherence problem
(B) Consistency problem
(C) Synchronization problem
(D) Conflict problem

11. : How does the “Write-Invalidate” protocol help in maintaining cache coherency?
(A) By invalidating other caches’ copies of a cache line when one cache writes to it
(B) By writing data to all caches
(C) By locking a cache line during write operations
(D) By updating all caches with the new data

12. : What is a “snoopy” cache coherency protocol?
(A) A protocol where caches monitor (snoop) the shared communication bus for transactions
(B) A protocol where caches are directly connected without a bus
(C) A protocol that uses software to manage cache coherency
(D) A protocol that requires no inter-cache communication

13. : What role does the “bus” play in a snoopy cache coherency protocol?
(A) It allows caches to broadcast and listen to memory transactions to maintain coherency
(B) It stores data for caches
(C) It manages cache replacement policies
(D) It increases the speed of cache access

14. : Which of the following is a key characteristic of the MSI cache coherency protocol?
(A) It uses Modified, Shared, and Invalid states
(B) It includes an Owner state
(C) It is an extension of the MESI protocol
(D) It uses a write-through policy

15. : In a system using cache coherency protocols, what is the purpose of the “bus invalidation” mechanism?
(A) To ensure that all caches invalidate their copies of a cache line when it is written to by another cache
(B) To synchronize the data between different caches
(C) To manage cache line replacement
(D) To increase cache line size

16. : What does “write-through” cache policy ensure?
(A) All writes are immediately written to main memory as well as to the cache
(B) Writes are only made to the cache and are delayed for main memory updates
(C) Writes are made only if the cache line is modified
(D) Writes are made only to the main memory

17. : What problem arises when multiple processors have stale copies of data?
(A) Cache consistency problem
(B) Cache coherence problem
(C) Memory alignment problem
(D) Cache replacement problem

18. : Which protocol adds the “Dirty” state to handle cache coherence?
(A) MOESI
(B) MESI
(C) MSI
(D) MESIF

19. : What is the main function of the “Owner” state in the MOESI protocol?
(A) To allow a cache to keep a modified copy of the cache line and be responsible for updating main memory
(B) To ensure that a cache line is only read
(C) To ensure that a cache line is invalidated
(D) To make a cache line exclusive

20. : How does the “write-back” cache policy handle data changes?
(A) It writes data changes to the cache and only updates main memory when the cache line is evicted
(B) It writes data changes immediately to both the cache and main memory
(C) It delays all write operations until the system is idle
(D) It only updates the main memory and not the cache

21. : What does a “cache coherence protocol” typically manage?
(A) The consistency of data across multiple caches in a multiprocessor system
(B) The size and speed of the cache
(C) The physical memory layout
(D) The hardware design of the processor

22. : What is the impact of cache coherence issues on system performance?
(A) It can lead to increased latency and reduced throughput due to inconsistent data
(B) It can improve system performance by increasing cache hit rates
(C) It has no impact on system performance
(D) It simplifies the cache design

23. : In the MESI protocol, what is the role of the “Exclusive” state?
(A) To indicate that a cache line is held exclusively by one cache and is clean (not modified)
(B) To indicate that a cache line is dirty and modified
(C) To indicate that a cache line is shared with other caches
(D) To indicate that the cache line is invalid

24. : Which protocol is designed to handle cache coherency in systems with multiple processors and shared caches?
(A) MESI
(B) LRU
(C) FIFO
(D) MSI

25. : What does the “Invalid” state signify in a cache coherency protocol?
(A) The cache line is no longer valid and should not be used for reads or writes
(B) The cache line is shared among multiple caches
(C) The cache line is modified and needs to be written back to memory
(D) The cache line is exclusively held by a single cache

26. : How does the “write-invalidate” cache coherence protocol work?
(A) It invalidates other caches’ copies of a cache line when one cache writes to it
(B) It writes data to all caches
(C) It locks the cache line during write operations
(D) It synchronizes the data between caches

27. : What is the key difference between the MSI and MESI cache coherency protocols?
(A) MESI includes an additional “Exclusive” state, while MSI does not
(B) MSI includes an “Owner” state
(C) MESI does not use an “Invalid” state
(D) MSI includes a “Shared” state

28. : What is the purpose of the “snooping” mechanism in cache coherence protocols?
(A) To monitor bus transactions and ensure cache coherency
(B) To synchronize the clock speeds of multiple caches
(C) To manage cache replacement policies
(D) To increase the size of the cache

29. : What happens if a processor writes to a cache line while another processor is reading from it?
(A) The cache line in the other processor’s cache may become stale if not properly invalidated
(B) Both processors will have updated cache lines
(C) The system will automatically synchronize the caches
(D) The reading processor will be locked until the write completes

30. : What does the “bus read” operation do in the context of cache coherence?
(A) It allows a cache to obtain the latest version of a cache line from the bus
(B) It invalidates the cache line in all caches
(C) It writes data to the main memory
(D) It updates the cache line in all caches

31. : In the context of cache coherence, what is the primary role of a “cache coherence controller”?
(A) To manage and enforce cache coherency protocols across multiple caches
(B) To increase the speed of cache memory
(C) To handle cache replacement policies
(D) To synchronize the clock speeds of multiple processors

32. : What is the purpose of the “Shared” state in cache coherency protocols?
(A) To indicate that a cache line may be present in multiple caches and is not modified
(B) To indicate that the cache line is exclusively held by one cache
(C) To indicate that the cache line is dirty and needs to be written back
(D) To indicate that the cache line is invalid

33. : What issue does a “cache coherence protocol” specifically address?
(A) Ensuring that all caches have a consistent view of memory in a multiprocessor system
(B) Managing the physical memory layout
(C) Increasing the speed of the cache
(D) Handling cache replacement policies

34. : What does the “write-back” policy ensure in cache management?
(A) Data changes are written back to main memory only when the cache line is evicted
(B) All data changes are immediately written to both cache and main memory
(C) Data changes are delayed until the system is idle
(D) Data changes are not written to main memory

35. : In the MOESI protocol, what does the “Exclusive” state indicate?
(A) The cache line is present only in one cache and is not modified
(B) The cache line is dirty and modified
(C) The cache line is shared with other caches
(D) The cache line is invalid

36. : Which cache coherence protocol includes the “Modified,” “Exclusive,” “Shared,” and “Invalid” states?
(A) MESI
(B) MOESI
(C) MSI
(D) MOSI

37. : What does a cache coherence protocol’s “write-update” operation do?
(A) It updates all caches with the new value of a cache line when it is modified
(B) It invalidates the cache line in other caches
(C) It writes data changes to the main memory
(D) It locks the cache line during write operations

38. : What is the primary advantage of the “write-invalidate” protocol over the “write-update” protocol?
(A) It reduces the amount of data traffic by invalidating other copies rather than updating them
(B) It increases the consistency of data across caches
(C) It ensures faster data synchronization
(D) It reduces the complexity of cache management

39. : In a system with multiple caches, what does the “cache coherence” mechanism prevent?
(A) Data inconsistencies between different caches
(B) Cache line replacement
(C) Cache line expansion
(D) Cache memory leaks

40. : What is a common feature of both MESI and MOESI protocols?
(A) Both include mechanisms to maintain cache coherency in multiprocessor systems
(B) Both use only the “Modified” and “Shared” states
(C) Both protocols are used for single-processor systems
(D) Both require no inter-cache communication

41. : In the context of cache coherence, what does “bus transaction” refer to?
(A) Operations that involve communication between caches over the system bus to maintain coherency
(B) The transfer of data between cache and main memory
(C) The management of cache replacement policies
(D) The synchronization of cache line sizes

42. : What is the role of the “cache coherence controller” in multiprocessor systems?
(A) To enforce the cache coherency protocols and manage cache coherency across multiple caches
(B) To manage cache line sizes and speeds
(C) To increase the physical size of the cache
(D) To handle data encryption in caches

43. : How does the “Modified” state in the MESI protocol affect other caches?
(A) It requires other caches to invalidate their copies of the cache line
(B) It updates all copies of the cache line in other caches
(C) It ensures that all caches have the same data
(D) It allows multiple caches to share the modified data

44. : What is a key challenge that cache coherency protocols address?
(A) Ensuring that all caches have a consistent view of memory and data
(B) Increasing the speed of cache access
(C) Reducing cache line size
(D) Managing cache replacement policies

45. : What impact does the “write-back” policy have on system performance?
(A) It can reduce memory traffic by deferring writes to main memory until cache lines are evicted
(B) It increases the frequency of writes to main memory
(C) It simplifies cache management
(D) It reduces the amount of data in the cache

46. : Which state in the MESI protocol indicates that a cache line is held exclusively by one cache and is clean?
(A) Exclusive
(B) Modified
(C) Shared
(D) Invalid

47. : What is the key advantage of the “MOESI” protocol over the “MESI” protocol?
(A) The addition of the “Owner” state allows for more efficient handling of modified data
(B) The exclusion of the “Exclusive” state simplifies protocol management
(C) The “MESI” protocol includes the “Owner” state
(D) The “MOESI” protocol uses a write-through policy

48. : In a multiprocessor system, what does a “cache coherence violation” indicate?
(A) A situation where different caches have inconsistent data for the same memory address
(B) A problem with cache line replacement
(C) An issue with cache size management
(D) A discrepancy in cache line speed

49. : What role does the “bus” play in maintaining cache coherency?
(A) It facilitates communication between caches to synchronize data and enforce coherency
(B) It stores cache data
(C) It manages the speed of cache access
(D) It handles cache replacement policies

50. : Which state in the MOESI protocol is responsible for ensuring that modified data is eventually written back to main memory?
(A) Owner
(B) Modified
(C) Exclusive
(D) Shared

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