Which of the following statements are true? A. In the write-through policy,…

Answer: Statements C and D are correct; A and B are incorrect.

• Statement A — False. In the write-through policy, a write updates both the cache and main memory immediately; it is not true that only the cache is updated.

• Statement B — False. In the write-back policy, writes update the cache first and the main memory is updated later (for example when the cache line is evicted).

• Statement C — True. Cache coherence problems arise in multiprocessor systems with private caches because multiple processors can hold copies of the same writable data, leading to inconsistent views unless coherence is maintained.

• Statement D — True. Cache coherence can be solved by hardware-only schemes (for example cache coherence protocols such as MESI); software approaches also exist, but a hardware-only solution is possible.

Key points:

• Write-through: every write is made to both the cache and main memory immediately, simplifying coherence at the cost of higher write traffic.

• Write-back: writes update only the cache and defer writing to main memory until eviction, improving performance but requiring coherence mechanisms.

• Hardware coherence protocols (for example MESI) are a common hardware-only solution that ensure a consistent view of shared data across private caches.