Practice advanced Cache Memory MCQ questions covering set associative mapping, hit ratio calculations, cache miss types, multilevel cache hierarchy, replacement policies, inclusion property, and write policies. Useful for GATE, IBPS IT Officer, university semester exams, and Computer Organization & Architecture (COA) preparation.
Topic: Computer Organization & Architecture (COA) – Cache Memory | Set: 3
Difficulty: Hard | Total Questions: 15
Cache Memory MCQ Questions
Q1: Consider a 64 KB 4-way set associative cache with 16-byte blocks. How many bits are in the “Index” field for a 32-bit address?
A. 10 bits
B. 12 bits
C. 14 bits
D. 16 bits View Answer
View Answern & Explanation
Answer: A. 10 bits
Explanation: Blocks = 64KB / 16B = 4096. Sets = 4096 / 4 = 1024 = 210. Therefore, Index = 10 bits.
Q2: In the average access time formula Tavg = h × C + (1-h) × M, what does M represent?
A. Cache access time
B. Miss penalty (Main memory access time)
C. Hit ratio
D. Number of sets View Answer
View Answern & Explanation
Answer: B. Miss penalty (Main memory access time)
Explanation: M represents the time required to retrieve data from the next level of memory after a cache miss occurs.
Q3: A “Lockup-free” cache is beneficial because it:
A. Prevents the CPU from crashing
B. Allows the cache to handle subsequent requests while a miss is being serviced
C. Encrypts the data automatically
D. Uses no power during idle states View Answer
View Answern & Explanation
Answer: B. Allows the cache to handle subsequent requests while a miss is being serviced
Explanation: Non-blocking or lockup-free caches allow multiple outstanding misses and concurrent cache operations.
Q4: If the hit time is 1 cycle and the miss penalty is 100 cycles, what hit rate is needed to achieve an average access time of 2 cycles?
A. 90%
B. 95%
C. 99%
D. 50% View Answer
View Answern & Explanation
Answer: C. 99%
Explanation: 2 = h × 1 + (1-h) × 100 → 99h = 98 → h ≈ 0.99.
Q5: In a multilevel cache, the “Inclusion Property” means:
A. L1 data is a subset of L2 data
B. L2 data is a subset of L1 data
C. L1 and L2 have completely different data
D. L1 is always larger than L2 View Answer
View Answern & Explanation
Answer: A. L1 data is a subset of L2 data
Explanation: Inclusion ensures every block present in L1 is also available in L2 cache.
Q6: Which of the following causes a “Capacity Miss”?
A. Multiple blocks mapping to the same set
B. The cache is too small to hold all blocks needed by the program
C. Accessing a block for the very first time
D. A write-through violation View Answer
View Answern & Explanation
Answer: B. The cache is too small to hold all blocks needed by the program
Explanation: Capacity misses occur when the working set exceeds the cache size.
Q7: Compulsory misses (Cold Start misses) can be reduced by:
A. Increasing cache associativity
B. Using a larger block size
C. Increasing the total cache size
D. Changing from write-back to write-through View Answer
View Answern & Explanation
Answer: B. Using a larger block size
Explanation: Larger blocks preload nearby data that may soon be accessed.
Q8: In a 32-bit address system with a 2-way set associative cache of 16KB and 64-byte blocks, find the Tag bits.
A. 17
B. 19
C. 20
D. 25 View Answer
View Answern & Explanation
Answer: B. 19
Explanation: Blocks = 16KB / 64B = 256. Sets = 256 / 2 = 128 = 27. Offset = 6 bits. Tag = 32 – 7 – 6 = 19.
Q9: Which replacement policy is optimal but impossible to implement in practice?
A. LRU
B. MIN (Belady’s Algorithm)
C. FIFO
D. MRU View Answer
View Answern & Explanation
Answer: B. MIN (Belady’s Algorithm)
Explanation: It requires future knowledge of memory accesses, making it impractical in real systems.
Q10: A write-allocate policy is usually paired with:
A. Write-through
B. Write-back
C. Direct mapping only
D. Fully associative mapping only View Answer
View Answern & Explanation
Answer: B. Write-back
Explanation: Write-allocate fetches blocks into cache during write misses, which works efficiently with write-back caches.
Q41: The “Miss Rate” of a cache is 5%. What is the Hit Ratio?
A. 0.05
B. 0.50
C. 0.95
D. 1.05
View Answern & Explanation
Answer: C
Explanation: Hit Ratio + Miss Rate = 1; therefore, 1 – 0.05 = 0.95.
Q42: Which phenomenon describes the scenario where L1 and L2 caches work on different data to maximize total storage?
A. Inclusion
B. Exclusion
C. Coherence
D. Write-allocation
View Answern & Explanation
Answer: B
Explanation: Exclusive caches ensure that a block resides in only one level of the cache hierarchy at a time.
Q43: For a 64-way set associative cache, the mapping is effectively:
A. Direct mapping
B. Fully associative mapping
C. Close to fully associative mapping
D. Close to direct mapping
View Answern & Explanation
Answer: C
Explanation: High associativity behaves similarly to fully associative mapping as the number of slots in a set increases.
Q44: What is the “Tag” in a cache used for?
A. To identify the specific byte in a block
B. To identify which main memory block is currently in the cache slot
C. To store the data itself
D. To count the number of hits
View Answern & Explanation
Answer: B
Explanation: The tag bits are compared with the address bits to determine if the requested block is present.
Q45: A “Sector Cache” is designed to:
A. Reduce tag overhead by associating one tag with multiple data blocks
B. Only store data from the hard drive sectors
C. Replace LRU with a simpler logic
D. Speed up write-through operations
View Answern & Explanation
Answer: A
Explanation: Sector caches use a single tag for a large “sector” which is divided into smaller “blocks” or “chunks”.
Conclusion
These advanced Cache Memory MCQ questions covered hit ratio calculations, cache mapping techniques, inclusion and exclusion properties, cache misses, replacement policies, and write policies. Regular practice of these concepts is essential for Computer Organization and Architecture (COA), GATE, university semester exams, and competitive technical examinations.
Fore theory and concepts, refer to Cache Memory in Computer Organization.