How does locality of reference make cache memory effective?

Cache memory is effective because it leverages the principle of locality of reference, which observes that a central processing unit (CPU) tends to access the same set of memory locations repeatedly over a short period.

Because cache is a smaller, faster memory system located closer to the CPU than main memory, it stores copies of these frequently used instructions and data. When the CPU needs information, it checks the cache first. If the data is present—a "cache hit"—the CPU retrieves it much faster than it could from the slower main memory. By keeping the most relevant information readily available, the cache significantly reduces the time the CPU spends waiting for data, thereby improving overall system performance.1