Why processors have cache memory and how it works

Caching was invented to solve a significant problem. In the early decades of computing, main memory was extremely slow and incredibly expensive — but CPUs weren’t particularly fast, either. Starting in the 1980s, the gap began to widen very quickly. Microprocessor clock speeds took off, but memory access times improved far less dramatically. As this gap grew, it became increasingly clear that a new type of fast memory was needed to bridge the gap.