Which cache miss occurs on the first access to a data block that has never been loaded into the cache?

• A. Compulsory
• B. Capacity
• C. Conflict
• D. Coherence

Answer: (A)

When a data block is requested for the first time and it isn’t present in the cache at all, the miss is known as a compulsory (cold) miss. This happens because the data has never been loaded into the cache yet, so the system must fetch it from a lower level of memory or main memory. It’s called compulsory because it’s inevitable on the first access to any block.

This differs from capacity misses, which occur when the cache cannot hold all the working data even if it’s been loaded before, forcing evictions due to limited space. Conflict misses arise from the cache’s mapping scheme, where multiple blocks compete for the same cache set and cause evictions. Coherence misses happen in multi-core systems when another processor invalidates or updates a cache line, causing a miss when the line is accessed.

So, the first-ever access to a data block not yet loaded into the cache is a compulsory miss.