The performance of cache memory is frequently measured in terms of a quantity called ______.

The correct answer is C, Hit ratio. Cache memory is the small, very fast memory placed between the processor and main memory that keeps the data the processor is most likely to need next. When the processor finds the word it wants in the cache it is called a hit, and when it does not it is a miss that must be fetched from slower main memory. The hit ratio is the number of hits divided by the total number of memory references, so a higher hit ratio means a faster system; it is the standard measure of cache performance. A is wrong because a register is a storage location inside the CPU, not a measure. B is wrong because associative mapping is a way of placing blocks in the cache. D is wrong because set-associative mapping is likewise a mapping technique, not a performance figure. Exam tip: hit ratio = hits ÷ total references; cache mapping types are direct, associative and set-associative.