What is a CPU cache used for?

• A. Small, fast memory storing frequently used data to speed up access.
• B. A large storage area on disk.
• C. A cache is a secondary memory with slow speed.
• D. It is a type of CPU register that holds instructions.

Answer: (A)

The main idea is that a CPU cache is small, fast memory placed close to the processor to hold data and instructions the CPU expects to reuse soon. By keeping frequently used items ready in the cache, the processor can fetch them much quicker than from main memory, reducing latency and speeding up execution. This relies on locality of reference: programs tend to reuse the same data or nearby data within a short time, so a nearby fast copy pays off. Cache levels (L1, L2, L3) balance speed and size, with the fastest caches being smallest and closest to the CPU.

So, the description matches: small, fast memory storing frequently used data to speed up access. Large storage on disk is persistent but slow, not cache. A cache isn’t a slow secondary memory, and it isn’t simply a CPU register holding instructions—the cache is separate fast memory that serves the CPU by reducing access times to data and instructions.